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{{Short description|Form of precipitation}}
{{Redirect-several|Rain|Rainy|Rainfall|Rainwater}}
{{Pp-semi-indef}}
{{Pp-move}}
[[File:Hard rain on a roof.jpg|thumb|upright=1.35|Heavy rainfall on a roof]]
{{Weather}}
'''Rain''' is a form of [[
The major cause of rain production is moisture moving along three-dimensional zones of temperature and moisture contrasts known as [[weather fronts]]. If enough moisture and upward motion is present, [[precipitation]] falls from [[convection|convective]] clouds (those with strong upward vertical motion) such as [[cumulonimbus]] (thunder clouds) which can organize into narrow [[rainbands]]. In mountainous areas, heavy precipitation is possible where [[upslope flow]] is maximized within [[windward]] sides of the [[terrain]] at elevation which forces moist air to condense and fall out as rainfall along the sides of mountains. On the [[leeward]] side of mountains, desert climates can exist due to the dry air caused by downslope flow which causes heating and drying of the [[air mass]]. The movement of the [[monsoon trough]], or [[Intertropical Convergence Zone]], brings [[wet season|rainy seasons]] to [[savannah]] [[clime]]s.
The [[urban heat island]] effect leads to increased rainfall, both in amounts and intensity, downwind of cities. [[Global warming]] is also causing changes in the precipitation pattern, including wetter conditions across eastern North America and drier conditions in the tropics. Antarctica is the driest continent. The globally averaged annual precipitation over land is {{convert|715|mm|in|abbr=on}}, but over the whole Earth, it is much higher at {{convert|990|mm|in|abbr=on}}.<ref>{{cite web |url=http://www.planetguide.net/book/chapter_2/water_cycle.html |title=The Water Cycle |publisher=Planetguide.net |access-date=26 December 2011 |archive-url=https://web.archive.org/web/20111226143942/http://www.planetguide.net/book/chapter_2/water_cycle.html |archive-date=26 December 2011 }}</ref> [[Climate classification]] systems such as the [[Köppen climate classification|Köppen classification]] system use average annual rainfall to help differentiate between differing climate regimes. Rainfall is measured using [[rain gauge]]s. Rainfall amounts can be estimated by [[weather radar]].
==Formation==
===Water-saturated air===
Air contains water vapor, and the amount of water in a given mass of dry air, known as the ''mixing ratio'', is measured in grams of water per kilogram of dry air (g/kg).<ref>{{cite web|author=Steve Kempler|year=2009|url=http://daac.gsfc.nasa.gov/PIP/shtml/atmospheric_water_vapor_or_humidity.shtml|title=Parameter information page|publisher=[[NASA]] [[Goddard Space Flight Center]]|access-date=27 December 2008 |archive-url = https://web.archive.org/web/20071126083414/http://daac.gsfc.nasa.gov/PIP/shtml/atmospheric_water_vapor_or_humidity.shtml |archive-date = 26 November 2007}}</ref><ref>{{cite book|url=http://www.atmos.washington.edu/~stoeling/WH-Ch03.pdf|page=80|access-date=30 January 2010|date=12 September 2005|author=Mark Stoelinga|title=Atmospheric Thermodynamics|publisher=University of Washington|archive-url=https://web.archive.org/web/20100602004341/http://www.atmos.washington.edu/~stoeling/WH-Ch03.pdf|archive-date=2 June 2010}}</ref> The amount of moisture in the air is also commonly reported as [[relative humidity]]; which is the percentage of the total water vapor air can hold at a particular air temperature.<ref>{{cite web|url=http://amsglossary.allenpress.com/glossary/search?p=1&query=relative+humidity&submit=Search|author=Glossary of Meteorology|date=June 2000|access-date=29 January 2010|publisher=[[American Meteorological Society]]|title=Relative Humidity|archive-url=https://web.archive.org/web/20110707113357/http://amsglossary.allenpress.com/glossary/search?p=1&query=relative+humidity&submit=Search|archive-date=7 July 2011}}</ref> How much water vapor a parcel of air can contain before it becomes saturated (100% relative humidity) and forms into a [[cloud]] (a group of visible tiny water or ice [[particle]]s suspended above the Earth's surface)<ref>{{cite web|url=http://amsglossary.allenpress.com/glossary/search?id=cloud1|author=Glossary of Meteorology|date=June 2000|access-date=29 January 2010|publisher=[[American Meteorological Society]]|title=Cloud|archive-url=https://web.archive.org/web/20081220034950/http://amsglossary.allenpress.com/glossary/search?id=cloud1|archive-date=20 December 2008}}</ref> depends on its temperature. Warmer air can contain more water vapor than cooler air before becoming saturated. Therefore, one way to saturate a parcel of air is to cool it. The [[dew point]] is the temperature to which a parcel must be cooled in order to become saturated.<ref>{{cite web|author=Naval Meteorology and Oceanography Command |year=2007 |url=http://www.navmetoccom.navy.mil/pao/Educate/WeatherTalk2/indexatmosp.htm |title=Atmospheric Moisture |publisher=United States Navy |access-date=27 December 2008 |archive-url=https://web.archive.org/web/20090114165909/http://www.navmetoccom.navy.mil/pao/Educate/WeatherTalk2/indexatmosp.htm |archive-date=14 January 2009 }}</ref>
There are four main mechanisms for cooling the air to its dew point: adiabatic cooling, conductive cooling, radiational cooling, and evaporative cooling. [[Adiabatic lapse rate#Dry adiabatic lapse rate|Adiabatic cooling]] occurs when air rises and expands.<ref>{{cite web|author=Glossary of Meteorology|year=2009|url=http://amsglossary.allenpress.com/glossary/search?id=adiabatic-process1|title=Adiabatic Process|publisher=[[American Meteorological Society]]|access-date=27 December 2008|archive-url=https://web.archive.org/web/20071017213229/http://amsglossary.allenpress.com/glossary/search?id=adiabatic-process1|archive-date=17 October 2007}}</ref> The air can rise due to [[convection]], large-scale atmospheric motions, or a physical barrier such as a mountain ([[orographic lift]]). Conductive cooling occurs when the air comes into contact with a colder surface,<ref>{{cite web|author=TE Technology, Inc|year=2009|url=http://www.tetech.com/Cold-Plate-Coolers.html|title=Peltier Cold Plate|access-date=27 December 2008|url-status=live|archive-url=https://web.archive.org/web/20090101113417/http://www.tetech.com/Cold-Plate-Coolers.html|archive-date=1 January 2009}}</ref> usually by being blown from one surface to another, for example from a liquid water surface to colder land. Radiational cooling occurs due to the emission of [[Thermal radiation|infrared radiation]], either by the air or by the surface underneath.<ref>{{cite web|author=Glossary of Meteorology|year=2009|url=http://amsglossary.allenpress.com/glossary/search?p=1&query=radiational+cooling&submit=Search|title=Radiational cooling|publisher=[[American Meteorological Society]]|access-date=27 December 2008|archive-url=https://web.archive.org/web/20110512161339/http://amsglossary.allenpress.com/glossary/search?p=1&query=radiational+cooling&submit=Search|archive-date=12 May 2011}}</ref> Evaporative cooling occurs when moisture is added to the air through evaporation, which forces the air temperature to cool to its [[wet-bulb temperature]], or until it reaches saturation.<ref>{{cite web|author=Robert Fovell |year=2004 |url=http://www.atmos.ucla.edu/~fovell/AS3downloads/saturation.pdf |title=Approaches to saturation |publisher=[[UCLA|University of California in Los Angeles]] |access-date=7 February 2009 |archive-url=https://web.archive.org/web/20090225074155/http://www.atmos.ucla.edu/~fovell/AS3downloads/saturation.pdf |archive-date=25 February 2009 }}</ref>
The main ways water vapor is added to the air are wind convergence into areas of upward motion,<ref name="convection">{{cite book|author=Robert Penrose Pearce|year=2002|url=https://books.google.com/books?id=QECy_UBdyrcC&pg=PA66|title=Meteorology at the Millennium|publisher=Academic Press|page=66|isbn=978-0-12-548035-2|access-date=2 January 2009}}</ref> precipitation or virga falling from above,<ref>{{cite web|website=[[National Weather Service]] |___location=Spokane, WA |year=2009|url=http://www.wrh.noaa.gov/otx/outreach/ttalk/virga.php|title=Virga and Dry Thunderstorms|access-date=2 January 2009 |archive-url=https://web.archive.org/web/20090522112015/http://www.wrh.noaa.gov/otx/outreach/ttalk/virga.php|archive-date=22 May 2009}}</ref> daytime heating evaporating water from the surface of oceans, water bodies or wet land,<ref>{{cite web|author1=Bart van den Hurk |author2=Eleanor Blyth |name-list-style=amp |year=2008 |url=http://www.knmi.nl/~hurkvd/Loco_workshop/Workshop_report.pdf |title=Global maps of Local Land-Atmosphere coupling |publisher=KNMI |access-date=2 January 2009 |archive-url=https://web.archive.org/web/20090225074154/http://www.knmi.nl/~hurkvd/Loco_workshop/Workshop_report.pdf |archive-date=25 February 2009 }}</ref> transpiration from plants,<ref>{{cite web|author1=Krishna Ramanujan |author2=Brad Bohlander |name-list-style=amp |year=2002|url=http://www.gsfc.nasa.gov/topstory/20020926landcover.html|title=Landcover changes may rival greenhouse gases as cause of climate change|publisher=[[National Aeronautics and Space Administration]] [[Goddard Space Flight Center]]|access-date=2 January 2009 |archive-url = https://web.archive.org/web/20080603022239/http://www.gsfc.nasa.gov/topstory/20020926landcover.html |archive-date = 3 June 2008}}</ref> cool or dry air moving over warmer water,<ref>{{cite web|author=[[National Weather Service]] JetStream|year=2008|url=http://www.srh.weather.gov/srh/jetstream/synoptic/airmass.htm|title=Air Masses|access-date=2 January 2009|archive-url=https://web.archive.org/web/20081224062959/http://www.srh.weather.gov/srh/jetstream/synoptic/airmass.htm|archive-date=24 December 2008}}</ref> and lifting air over mountains.<ref name="MT">{{cite web|author=Michael Pidwirny |year=2008 |url=http://www.physicalgeography.net/fundamentals/8e.html |title=CHAPTER 8: Introduction to the Hydrosphere (e). Cloud Formation Processes |publisher=Physical Geography |access-date=1 January 2009 |archive-url=https://web.archive.org/web/20081220230524/http://www.physicalgeography.net/fundamentals/8e.html |archive-date=20 December 2008 }}</ref> Water vapor normally begins to condense on [[Cloud condensation nuclei|condensation nuclei]] such as dust, ice, and salt in order to form clouds. Elevated portions of weather fronts (which are three-dimensional in nature)<ref>{{cite web|url=http://amsglossary.allenpress.com/glossary/search?id=front1|author=Glossary of Meteorology|date=June 2000|access-date=29 January 2010|publisher=[[American Meteorological Society]]|title=Front|url-status=live|archive-url=https://web.archive.org/web/20110514090302/http://amsglossary.allenpress.com/glossary/search?id=front1|archive-date=14 May 2011}}</ref> force broad areas of upward motion within the Earth's atmosphere which form clouds decks such as [[altostratus]] or [[cirrostratus]].<ref name="DR">{{cite web|author=David Roth|title=Unified Surface Analysis Manual|access-date=22 October 2006|publisher=[[Hydrometeorological Prediction Center]]|url=http://www.wpc.ncep.noaa.gov/sfc/UASfcManualVersion1.pdf|url-status=live|archive-url=https://web.archive.org/web/20060929004553/http://www.hpc.ncep.noaa.gov/sfc/UASfcManualVersion1.pdf|archive-date=29 September 2006}}</ref> [[Stratus cloud|Stratus]] is a stable cloud deck which tends to form when a cool, stable air mass is trapped underneath a warm air mass. It can also form due to the lifting of [[Radiation fog|advection fog]] during breezy conditions.<ref>{{cite web|author=FMI|year=2007|url=http://www.zamg.ac.at/docu/Manual/SatManu/main.htm?/docu/Manual/SatManu/CMs/FgStr/backgr.htm|title=Fog And Stratus – Meteorological Physical Background|publisher=Zentralanstalt für Meteorologie und Geodynamik|access-date=7 February 2009|url-status=live|archive-url=https://web.archive.org/web/20110706085616/http://www.zamg.ac.at/docu/Manual/SatManu/main.htm?%2Fdocu%2FManual%2FSatManu%2FCMs%2FFgStr%2Fbackgr.htm|archive-date=6 July 2011}}</ref>
===Coalescence and fragmentation===
[[File:Raindrops sizes.svg|upright=1.3|alt=Diagram showing that very small rain drops are almost spherical in shape. As drops become larger, they become flattened on the bottom, like a hamburger bun. Very large rain drops are split into smaller ones by air resistance which makes them increasingly unstable.|thumb|The shape of raindrops depending upon their size:
{{Ordered list | list_style_type=upper-alpha
|Contrary to popular belief, raindrops are never tear-shaped.
|Very small raindrops are almost spherical.
|Larger raindrops become flattened at the bottom due to air resistance.
|Large raindrops have a large amount of air resistance, and begin to become unstable.
|Very large raindrops split into smaller raindrops due to air resistance.
}}
]]
[[Coalescence (meteorology)|Coalescence]] occurs when water droplets fuse to create larger water droplets.<ref>{{Cite journal |last1=Klyuzhin |first1=Ivan S. |last2=Ienna |first2=Federico |last3=Roeder |first3=Brandon |last4=Wexler |first4=Adam |last5=Pollack |first5=Gerald H. |date=2010-11-11 |title=Persisting water droplets on water surfaces |journal=The Journal of Physical Chemistry. B |volume=114 |issue=44 |pages=14020–14027 |doi=10.1021/jp106899k |issn=1520-5207 |pmc=3208511 |pmid=20961076}}</ref> Air resistance typically causes the water droplets in a cloud to remain stationary. When air turbulence occurs, water droplets collide, producing larger droplets.<ref>{{Cite web |title=Cloud Development |url=https://www.weather.gov/source/zhu/ZHU_Training_Page/clouds/cloud_development/clouds.htm |access-date=2025-07-08 |website=National Weather Service}}</ref><ref>{{Cite journal |last1=Benmoshe |first1=N. |last2=Pinsky |first2=M. |last3=Pokrovsky |first3=A. |last4=Khain |first4=A. |date=2012-03-27 |title=Turbulent effects on the microphysics and initiation of warm rain in deep convective clouds: 2-D simulations by a spectral mixed-phase microphysics cloud model |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2011JD016603 |journal=Journal of Geophysical Research: Atmospheres |language=en |volume=117 |issue=D6 |article-number=2011JD016603 |doi=10.1029/2011JD016603 |bibcode=2012JGRD..117.6220B |issn=0148-0227|url-access=subscription }}</ref>
As these larger water droplets descend, coalescence continues, so that drops become heavy enough to overcome air resistance and fall as rain. Coalescence generally happens most often in clouds above freezing (in their top) and is also known as the warm rain process.<ref>{{cite web|author=Glossary of Meteorology|date=June 2000|url=http://amsglossary.allenpress.com/glossary/search?id=warm-rain-process1|title=Warm Rain Process|access-date=15 January 2010|publisher=[[American Meteorological Society]]|archive-url=https://web.archive.org/web/20121209205815/http://amsglossary.allenpress.com/glossary/search?id=warm-rain-process1|archive-date=9 December 2012}}</ref> In clouds below freezing, when ice crystals gain enough mass they begin to fall. This generally requires more mass than coalescence when occurring between the crystal and neighboring water droplets. This process is temperature dependent, as supercooled water droplets only exist in a cloud that is below freezing. In addition, because of the great temperature difference between cloud and ground level, these ice crystals may melt as they fall and become rain.<ref>{{cite web|author=Paul Sirvatka|year=2003|url=http://weather.cod.edu/sirvatka/bergeron.html|title=Cloud Physics: Collision/Coalescence; The Bergeron Process|publisher=[[College of DuPage]]|access-date=1 January 2009|url-status=live|archive-url=https://web.archive.org/web/20120717083651/http://weather.cod.edu/sirvatka/bergeron.html|archive-date=17 July 2012}}</ref>
Raindrops have sizes ranging from {{convert|0.1|to|9|mm|in|abbr=on}} mean diameter but develop a tendency to break up at larger sizes. Smaller drops are called cloud droplets, and their shape is spherical. As a raindrop increases in size, its shape becomes more oblate, with its largest cross-section facing the oncoming airflow. Large rain drops become increasingly flattened on the bottom, like [[hamburger]] buns; very large ones are shaped like [[parachute]]s.<ref>{{cite web |title = Bad Meteorology: Raindrops are shaped like teardrops |url = http://www.ems.psu.edu/~fraser/Bad/BadRain.html |author = Alistair B. Fraser |access-date = 7 April 2008 |date = 15 January 2003 |publisher = [[Pennsylvania State University]] |url-status=live |archive-url = https://web.archive.org/web/20120807041743/http://www.ems.psu.edu/~fraser/Bad/BadRain.html |archive-date = 7 August 2012 }}</ref><ref name="Villermaux" /> Contrary to popular belief, their shape does not resemble a teardrop.<ref>{{cite web|author=United States Geological Survey|year=2009|url=http://ga.water.usgs.gov/edu/raindropshape.html|title=Are raindrops tear shaped?|publisher=[[United States Department of the Interior]]|access-date=27 December 2008|archive-url=https://web.archive.org/web/20120618130034/http://ga.water.usgs.gov/edu/raindropshape.html|archive-date=18 June 2012|author-link=United States Geological Survey}}</ref> The biggest raindrops on Earth were recorded over Brazil and the [[Marshall Islands]] in 2004 — some of them were as large as {{convert|10|mm|in|abbr=on}}. The large size is explained by condensation on large [[smoke]] particles or by collisions between drops in small regions with particularly high content of liquid water.<ref>{{cite news | title = Monster raindrops delight experts | url = http://news.bbc.co.uk/2/hi/science/nature/3898305.stm | author = Paul Rincon | publisher = [[British Broadcasting Company]] | date = 16 July 2004 | access-date = 30 November 2009 | url-status=live | archive-url = https://web.archive.org/web/20100128203851/http://news.bbc.co.uk/2/hi/science/nature/3898305.stm | archive-date = 28 January 2010 }}</ref>
Raindrops associated with melting hail tend to be larger than other raindrops.<ref>{{cite web|author=Norman W. Junker|year=2008|url=http://www.wpc.ncep.noaa.gov/research/mcs_web_test_test_files/Page882.htm|title=An ingredients based methodology for forecasting precipitation associated with MCS's|publisher=[[Hydrometeorological Prediction Center]]|access-date=7 February 2009|url-status=live|archive-url=https://web.archive.org/web/20130426035605/http://www.wpc.ncep.noaa.gov/research/mcs_web_test_test_files/Page882.htm|archive-date=26 April 2013}}</ref>
Intensity and duration of rainfall are usually inversely related, i.e., high-intensity storms are likely to be of short duration and low-intensity storms can have a long duration.<ref name="JS">{{cite web|author1=J. S. Oguntoyinbo |author2=F. O. Akintola |name-list-style=amp |year=1983 |url=http://www.cig.ensmp.fr/~iahs/redbooks/a140/iahs_140_0063.pdf |title=Rainstorm characteristics affecting water availability for agriculture |publisher=IAHS Publication Number 140 |access-date=27 December 2008 |archive-url=https://web.archive.org/web/20090205200119/http://www.cig.ensmp.fr/~iahs/redbooks/a140/iahs_140_0063.pdf |archive-date=5 February 2009 }}</ref><ref>{{cite journal|author=Robert A. Houze Jr|date=October 1997|title=Stratiform Precipitation in Regions of Convection: A Meteorological Paradox?|url=http://ams.allenpress.com/archive/1520-0477/78/10/pdf/i1520-0477-78-10-2179.pdf|journal=Bulletin of the American Meteorological Society|volume=78|issue=10|pages=2179–2196|bibcode=1997BAMS...78.2179H|doi=10.1175/1520-0477(1997)078<2179:SPIROC>2.0.CO;2|issn=1520-0477}}</ref>
===Droplet size distribution===
{{main|Raindrop size distribution}}
The final droplet size distribution is an [[exponential distribution]]. The number of droplets with diameter between <math>d</math> and <math>D+dD</math> per unit volume of space is <math>n(d) = n_0 e^{-d/\langle d \rangle} dD</math>. This is commonly referred to as the Marshall–Palmer law after the researchers who first characterized it.<ref name="Villermaux">{{cite journal |author=Emmanuel Villermaux, Benjamin Bossa |title=Single-drop fragmentation distribution of raindrops |url=https://www.irphe.fr/~fragmix/publis/VB2009.pdf |journal=Nature Physics |date=September 2009 |volume=5 |pages=697–702 |doi=10.1038/NPHYS1340 |issue=9 |bibcode=2009NatPh...5..697V |last2=Bossa |url-status=live |archive-url=https://web.archive.org/web/20120305070416/https://www.irphe.fr/~fragmix/publis/VB2009.pdf |archive-date=5 March 2012 }}
*{{cite news |author=Victoria Gill |date=20 July 2009 |title=Why raindrops come in many sizes |work=BBC News |url=http://news.bbc.co.uk/2/hi/science/nature/8155883.stm}}</ref><ref>{{cite journal | last1 = Marshall | first1 = J. S. | last2 = Palmer | first2 = W. M. | year = 1948 | title = The distribution of raindrops with size | journal = Journal of Meteorology| volume = 5 | issue = 4| pages = 165–166 | doi=10.1175/1520-0469(1948)005<0165:tdorws>2.0.co;2| bibcode = 1948JAtS....5..165M | doi-access = free }}</ref> The parameters are somewhat temperature-dependent,<ref>{{cite journal |author1=Houze Robert A. |author2=Hobbs Peter V. |author3=Herzegh Paul H. |author4=Parsons David B. | year = 1979 | title = Size Distributions of Precipitation Particles in Frontal Clouds | journal = J. Atmos. Sci. | volume = 36 | issue = 1| pages = 156–162 | doi = 10.1175/1520-0469(1979)036<0156:SDOPPI>2.0.CO;2 |bibcode = 1979JAtS...36..156H | doi-access = free }}</ref> and the slope also scales with the rate of rainfall <math>\langle d \rangle^{-1}=41 R^{-0.21}</math> (d in centimeters and R in millimeters per hour).<ref name="Villermaux" />
Deviations can occur for small droplets and during different rainfall conditions. The distribution tends to fit averaged rainfall, while instantaneous size spectra often deviate and have been modeled as [[gamma distribution]]s.<ref>{{cite journal | last1 = Niu | first1 = Shengjie | last2 = Jia | first2 = Xingcan | last3 = Sang | first3 = Jianren | last4 = Liu | first4 = Xiaoli | last5 = Lu | first5 = Chunsong | last6 = Liu | first6 = Yangang | year = 2010 | title = Distributions of Raindrop Sizes and Fall Velocities in a Semiarid Plateau Climate: Convective versus Stratiform Rains | journal = J. Appl. Meteorol. Climatol. | volume = 49 | issue = 4| pages = 632–645 | doi = 10.1175/2009JAMC2208.1 | bibcode = 2010JApMC..49..632N | doi-access = free }}</ref> The distribution has an upper limit due to droplet fragmentation.<ref name="Villermaux" />
===Raindrop impacts===
{{Listen|filename=Bourne woods rain 2020-05-10 0804.mp3|title=Rain|description=Typical sound of rain|format=[[Ogg]]}}
Raindrops impact at their [[terminal velocity]], which is greater for larger drops due to their larger mass-to-drag ratio. At sea level and without wind, {{convert|0.5|mm|in|abbr=on}} [[drizzle]] impacts at {{convert|2|m/s|ft/s|abbr=on}} or {{convert|4.5|mph|km/h|abbr=on|order=flip}}, while large {{convert|5|mm|in|abbr=on}} drops impact at around {{convert|9|m/s|ft/s|abbr=on}} or {{convert|20|mph|km/h|abbr=on|order=flip}}.<ref>{{cite news |title = Falling raindrops hit 5 to 20 mph speeds |url = http://usatoday30.usatoday.com/news/science/wonderquest/2001-12-19-rain-drops.htm |work=USA Today |access-date=22 December 2013 |date=19 December 2001}}</ref>
Rain falling on loosely packed material such as newly fallen ash can produce dimples that can be fossilized, called [[raindrop impressions]].<ref>{{cite journal |author1=van der Westhuizen W.A. |author2=Grobler N.J. |author3=Loock J.C. |author4=Tordiffe E.A.W. | year = 1989| title = Raindrop imprints in the Late Archaean-Early Proterozoic Ventersdorp Supergroup, South Africa | journal = Sedimentary Geology | volume = 61 | issue = 3–4| pages = 303–309 | doi = 10.1016/0037-0738(89)90064-X |bibcode = 1989SedG...61..303V }}</ref> The air density dependence of the maximum raindrop diameter together with fossil raindrop imprints has been used to constrain the density of the air 2.7 billion years ago.<ref>{{cite journal | last1 = Som | first1 = Sanjoy M. | last2 = Catling | first2 = David C. | last3 = Harnmeijer | first3 = Jelte P. | last4 = Polivka | first4 = Peter M. | last5 = Buick | first5 = Roger | year = 2012| title = Air density 2.7 billion years ago limited to less than twice modern levels by fossil raindrop imprints | journal = Nature | volume = 484 | issue = 7394| pages = 359–362 | doi = 10.1038/nature10890 | pmid = 22456703 | bibcode = 2012Natur.484..359S | s2cid = 4410348 }}</ref> The [[Droplet#Sound|sound of raindrops]] hitting water is caused by bubbles of air [[Minnaert resonance|oscillating underwater]].<ref>{{cite journal |first1=Andrea |last1=Prosperetti |first2=Hasan N. |last2=Oguz |name-list-style=amp |author-link1=Andrea Prosperetti |year=1993 |title=The impact of drops on liquid surfaces and the underwater noise of rain |journal=Annual Review of Fluid Mechanics |volume=25 |pages=577–602 |doi=10.1146/annurev.fl.25.010193.003045 |bibcode=1993AnRFM..25..577P}}</ref><ref>{{cite web |url=http://ffden-2.phys.uaf.edu/311_fall2004.web.dir/Ryan_Rankin/bubble%20resonance.htm |title=Bubble Resonance |access-date=9 December 2006 |first=Ryan C. |last=Rankin |date=June 2005 |website=The Physics of Bubbles, Antibubbles, and all That |url-status=live |archive-url=https://web.archive.org/web/20120307180441/http://ffden-2.phys.uaf.edu/311_fall2004.web.dir/Ryan_Rankin/bubble%20resonance.htm |archive-date=7 March 2012}}</ref>
The [[METAR]] code for rain is RA, while the coding for rain showers is SHRA.<ref name="METAR">{{cite web|url=http://www.alaska.faa.gov/fai/afss/metar%20taf/sametara.htm |title=SA-METAR |author=Alaska Air Flight Service Station |publisher=[[Federal Aviation Administration]] |access-date=29 August 2009 |date=10 April 2007 |archive-url=https://web.archive.org/web/20090603094326/http://www.alaska.faa.gov/fai/afss/metar%20taf/sametara.htm |archive-date=3 June 2009 }}</ref>
==
{{Main|Virga}}
In certain conditions, precipitation may fall from a cloud but then evaporate or [[Sublimation (phase transition)|sublime]] before reaching the ground. This is termed [[virga]], also known as "fallstreaks" or "precipitation trails",<ref>{{cite book |url=http://amsglossary.allenpress.com/glossary/search?id=virga1 |title=Glossary of Meteorology |publisher=[[American Meteorological Society]] |year=2000 |isbn=1-878220-34-9 |archive-url=https://web.archive.org/web/20110606113939/http://amsglossary.allenpress.com/glossary/search?id=virga1 |archive-date=2011-06-06 |url-status=dead}}</ref> and also refers to an optical phenomenon where the brightness of precipitation appears to abruptly change under a cloud.<ref>{{Cite journal |last1=Fraser |first1=Alistair B. |last2=Bohren |first2=Craig F. |date=1992 |title=Is Virga Rain That Evaporates before Reaching the Ground? |url=http://journals.ametsoc.org/doi/10.1175/1520-0493(1992)1202.0.CO;2 |journal=Monthly Weather Review |language=en |volume=120 |issue=8 |pages=1565–1571 |doi=10.1175/1520-0493(1992)120<1565:IVRTEB>2.0.CO;2 |bibcode=1992MWRv..120.1565F |issn=0027-0644|url-access=subscription }}</ref> Virga is common in hot and arid climates,<ref>{{Cite journal |last1=Karle |first1=Nakul N. |last2=Sakai |first2=Ricardo K. |last3=Fitzgerald |first3=Rosa M. |last4=Ichoku |first4=Charles |last5=Mercado |first5=Fernando |last6=Stockwell |first6=William R. |date=2023-03-02 |title=Systematic analysis of virga and its impact on surface particulate matter observations |url=https://amt.copernicus.org/articles/16/1073/2023/ |journal=Atmospheric Measurement Techniques |language=English |volume=16 |issue=4 |pages=1073–1085 |doi=10.5194/amt-16-1073-2023 |bibcode=2023AMT....16.1073K |issn=1867-1381 |doi-access=free}}</ref> but has been recorded in the Arctic<ref>{{Cite report |url=https://meetingorganizer.copernicus.org/EGU25/EGU25-20517.html |title=Virga Detection Tool based on Micro Rain Radar in Arctic |last1=Saini |first1=Lekhraj |last2=Das |first2=Saurabh |last3=Murukesh |first3=Nuncio |date=2025-03-14 |publisher=Copernicus Meetings |issue=EGU25-20517 |doi=10.5194/egusphere-egu25-20517 |language=en |doi-access=free|url-access=subscription }}</ref> and Antarctica<ref>{{Cite journal |last1=Jullien |first1=Nicolas |last2=Vignon |first2=Étienne |last3=Sprenger |first3=Michael |last4=Aemisegger |first4=Franziska |last5=Berne |first5=Alexis |date=2020-05-27 |title=Synoptic conditions and atmospheric moisture pathways associated with virga and precipitation over coastal Adélie Land in Antarctica |url=https://tc.copernicus.org/articles/14/1685/2020/ |journal=The Cryosphere |language=English |volume=14 |issue=5 |pages=1685–1702 |doi=10.5194/tc-14-1685-2020 |bibcode=2020TCry...14.1685J |issn=1994-0416 |doi-access=free|hdl=20.500.11850/418970 |hdl-access=free }}</ref> and is known to occur on planets beyond Earth, including Mars<ref>{{cite web |date=2008-09-29 |title=NASA Mars Lander Sees Falling Snow, Soil Data Suggest Liquid Past |website=[[Jet Propulsion Laboratory]] |url=https://www.jpl.nasa.gov/news/nasa-mars-lander-sees-falling-snow-soil-data-suggest-liquid-past |access-date=2023-12-14}}</ref> and Venus.<ref>{{cite news |date=7 November 2005 |title=Planet Venus: Earth's 'evil twin' |url=http://news.bbc.co.uk/2/hi/science/nature/4335628.stm |publisher=[[BBC News]]}}</ref>
==Causes==
===Frontal activity===
{{Main|Weather fronts}}
Stratiform (a broad shield of precipitation with a relatively similar intensity) and dynamic precipitation (convective precipitation which is showery in nature with large changes in intensity over short distances) occur as a consequence of slow ascent of air in [[Synoptic scale meteorology|synoptic systems]] (on the order of cm/s), such as in the vicinity of [[cold front]]s and near and poleward of surface [[warm front]]s. Similar ascent is seen around [[tropical cyclone]]s outside the [[eye (cyclone)|eyewall]], and in comma-head precipitation patterns around [[mid-latitude cyclone]]s.<ref name="Geerts">{{cite web|author=B. Geerts|year=2002|url=http://www-das.uwyo.edu/~geerts/cwx/notes/chap10/con_str.html|title=Convective and stratiform rainfall in the tropics|publisher=[[University of Wyoming]]|access-date=27 November 2007|url-status=live|archive-url=https://web.archive.org/web/20071219010038/http://www-das.uwyo.edu/~geerts/cwx/notes/chap10/con_str.html|archive-date=19 December 2007}}</ref>
A wide variety of weather can be found along an occluded front, with thunderstorms possible, but usually, their passage is associated with a drying of the air mass. Occluded fronts usually form around mature low-pressure areas.<ref name=autogenerated3>{{cite web|author=David Roth|title=Unified Surface Analysis Manual|year=2006|access-date=22 October 2006|publisher=[[Hydrometeorological Prediction Center]]|url=http://www.wpc.ncep.noaa.gov/sfc/UASfcManualVersion1.pdf|url-status=live|archive-url=https://web.archive.org/web/20060929004553/http://www.hpc.ncep.noaa.gov/sfc/UASfcManualVersion1.pdf|archive-date=29 September 2006}}</ref> What separates rainfall from other precipitation types, such as [[ice pellets]] and snow, is the presence of a thick layer of air aloft which is above the melting point of water, which melts the frozen precipitation well before it reaches the ground. If there is a shallow near-surface layer that is below freezing, freezing rain (rain which freezes on contact with surfaces in subfreezing environments) will result.<ref>{{cite web|url=http://www.meted.ucar.edu/nwp/pcu3/cases/eta_05Dec02_ptype/page4.htm|title=Precipitation Type Forecasts in the Southeastern and Mid-Atlantic states|author=MetEd|date=14 March 2003|access-date=30 January 2010|publisher=[[University Corporation for Atmospheric Research]]|url-status=live|archive-url=https://web.archive.org/web/20110930084044/http://www.meted.ucar.edu/nwp/pcu3/cases/eta_05Dec02_ptype/page4.htm|archive-date=30 September 2011}}</ref> [[Hail]] becomes an increasingly infrequent occurrence when the freezing level within the atmosphere exceeds {{convert|11000|ft|m|abbr=on|order=flip}} above ground level.<ref name="mesoanal">{{cite web|url=http://www.crh.noaa.gov/lmk/soo/docu/SvrWx_MesoGuide.pdf|title=Meso-Analyst Severe Weather Guide|access-date=22 December 2013|publisher=[[National Oceanic and Atmospheric Administration]]|url-status=live|archive-url=https://web.archive.org/web/20111212211544/http://www.crh.noaa.gov/lmk/soo/docu/SvrWx_MesoGuide.pdf|archive-date=12 December 2011}}</ref>
===Convection===
[[File:Konvektionsregen.jpg|alt=Diagram showing that as moist air becomes heated more than its surroundings, it moves upward, resulting in brief rain showers.|thumb|right|Convective precipitation]]
[[File:Steigungsregen.jpg|alt=Diagram showing how moist air over the ocean rises and flows over the land, causing cooling and rain as it hits mountain ridges.|thumb|right|Orographic precipitation]]
[[Convection rain|Convective rain]], or showery precipitation, occurs from convective clouds (e.g., [[cumulonimbus]] or [[cumulus congestus]]). It falls as showers with rapidly changing intensity. Convective precipitation falls over a certain area for a relatively short time, as convective clouds have limited horizontal extent. Most precipitation in the [[tropics]] appears to be convective; however, it has been suggested that stratiform precipitation also occurs.<ref name="Geerts" /><ref>{{cite journal |author=Robert Houze |date=October 1997 |title=Stratiform Precipitation in Regions of Convection: A Meteorological Paradox? |journal=Bulletin of the American Meteorological Society |volume=78 |issue=10 |pages=2179–2196 |doi=10.1175/1520-0477(1997)078<2179:SPIROC>2.0.CO;2 |issn=1520-0477|bibcode = 1997BAMS...78.2179H |doi-access=free }}</ref> [[Graupel]] and [[hail]] indicate convection.<ref>{{cite web|author=Glossary of Meteorology|year=2009|url=http://amsglossary.allenpress.com/glossary/search?p=1&query=graupel&submit=Search|title=Graupel|publisher=[[American Meteorological Society]]|access-date=2 January 2009|archive-url=https://web.archive.org/web/20080308123814/http://amsglossary.allenpress.com/glossary/search?p=1&query=graupel&submit=Search|archive-date=8 March 2008}}</ref> In mid-latitudes, convective precipitation is intermittent and often associated with baroclinic boundaries such as [[cold front]]s, [[squall line]]s, and warm fronts.<ref>{{cite book|author=Toby N. Carlson|year=1991|url=https://books.google.com/books?id=2lIVAAAAIAAJ&pg=PA216|title=Mid-latitude Weather Systems|publisher=Routledge|page=216|isbn=978-0-04-551115-0}}</ref>
===Orographic effects===
{{Main|Orographic lift|Precipitation types (meteorology)|United States rainfall climatology}}
Orographic precipitation occurs on the [[windward]] side of mountains and is caused by the rising air motion of a large-scale flow of moist air across the mountain ridge, resulting in [[Adiabatic lapse rate|adiabatic]] cooling and condensation. In mountainous parts of the world subjected to relatively consistent winds (for example, the [[trade wind]]s), a more moist [[climate]] usually prevails on the windward side of a mountain than on the [[leeward]] or downwind side. Moisture is removed by orographic lift, leaving drier air (see [[katabatic wind]]) on the descending and generally warming, leeward side where a [[rain shadow]] is observed.<ref name="MT"/>
In [[Hawaii]], [[Mount Waiʻaleʻale]], on the island of Kauai, is notable for its extreme rainfall, as it is amongst the places in the world with the highest levels of rainfall, with {{convert|373|in|mm||abbr=on|order=flip}}.<ref>{{cite web
| url = https://wrcc.dri.edu/cgi-bin/cliMAIN.pl?hi6565
| title = Mt Waialeale 1047, Hawaii (516565)
| date = 1 August 2008
| website = WRCC
| publisher = NOAA
| access-date = 30 August 2018 }}</ref> Systems known as [[Kona storm]]s affect the state with heavy rains between October and April.<ref name="BIRCH">Steven Businger and Thomas Birchard Jr. [http://www.soest.hawaii.edu/MET/Faculty/businger/PDF/BowEchoPPR.pdf A Bow Echo and Severe Weather Associated with a Kona Low in Hawaii.] {{webarchive|url=https://web.archive.org/web/20070617001753/http://www.soest.hawaii.edu/MET/Faculty/businger/PDF/BowEchoPPR.pdf |date=17 June 2007 }} Retrieved on 22 May 2007.</ref> Local climates vary considerably on each island due to their topography, divisible into windward (''Ko{{okina}}olau'') and leeward (''Kona'') regions based upon ___location relative to the higher mountains. Windward sides face the east to northeast [[trade winds]] and receive much more rainfall; leeward sides are drier and sunnier, with less rain and less cloud cover.<ref>{{cite web|author=Western Regional Climate Center|year=2002|url=http://www.wrcc.dri.edu/narratives/HAWAII.htm|title=Climate of Hawaii|access-date=19 March 2008|url-status=live|archive-url=https://web.archive.org/web/20080314190922/http://www.wrcc.dri.edu/narratives/HAWAII.htm|archive-date=14 March 2008}}</ref>
In South America, the [[Andes]] mountain range blocks Pacific moisture that arrives in that continent, resulting in a desert-like climate just downwind across western Argentina.<ref name="Andes">{{cite book|author=Paul E. Lydolph|year=1985|url=https://books.google.com/books?id=bBjIuXHEgZ4C&pg=PA333|title=The Climate of the Earth|publisher=Rowman & Littlefield|page=333|isbn=978-0-86598-119-5}}</ref> The [[Sierra Nevada (U.S.)|Sierra Nevada]] range creates the same effect in North America forming the [[Great Basin]] and [[Mojave Desert]]s.<ref>{{cite book|author=Michael A. Mares|year=1999|url=https://books.google.com/books?id=g3CbqZtaF4oC&pg=PA252|title=Encyclopedia of Deserts|publisher=[[University of Oklahoma]] Press|page=252|isbn=978-0-8061-3146-7}}</ref><ref>{{cite web|author=Adam Ganson|year=2003|url=http://www.indiana.edu/~sierra/papers/2003/Ganson.html|title=Geology of Death Valley|publisher=[[Indiana University]]|access-date=7 February 2009|url-status=live|archive-url=https://web.archive.org/web/20091214072022/http://www.indiana.edu/~sierra/papers/2003/Ganson.html|archive-date=14 December 2009}}</ref>
===Within the tropics===
[[File:Cairns climate.svg|alt=Chart showing an Australian city with as much as 450 mm of rain in the winter months and less than 50 mm in the summer.|upright=1.25|thumb|Rainfall distribution by month in [[Cairns, Australia]], showing the extent of the wet season at that ___location]]
{{See also|Monsoon|Tropical cyclone}}
{{Main|Wet season}}
The wet, or rainy, season is the time of year, covering one or more months, when most of the average annual rainfall in a region falls.<ref>{{cite web|author=Glossary of Meteorology|year=2009|url=http://amsglossary.allenpress.com/glossary/search?id=rainy-season1|title=Rainy season|publisher=[[American Meteorological Society]]|access-date=27 December 2008|archive-url=https://web.archive.org/web/20090215203023/http://amsglossary.allenpress.com/glossary/search?id=rainy-season1|archive-date=15 February 2009}}</ref> The term ''green season'' is also sometimes used as a [[euphemism]] by tourist authorities.<ref>{{cite web|author=Costa Rica Guide|year=2005|url=http://costa-rica-guide.com/when.htm|title=When to Travel to Costa Rica|publisher=ToucanGuides|access-date=27 December 2008|url-status=live|archive-url=https://web.archive.org/web/20081207191204/http://costa-rica-guide.com/when.htm|archive-date=7 December 2008}}</ref> Areas with wet seasons are dispersed across portions of the [[tropics]] and [[subtropics]].<ref>{{cite web|author=Michael Pidwirny|year=2008|url=http://www.physicalgeography.net/fundamentals/9k.html|title=CHAPTER 9: Introduction to the Biosphere|publisher=PhysicalGeography.net|access-date=27 December 2008|url-status=live|archive-url=https://web.archive.org/web/20090101052056/http://www.physicalgeography.net/fundamentals/9k.html|archive-date=1 January 2009}}</ref> [[Savanna]] climates and areas with [[monsoon]] regimes have wet summers and dry winters. Tropical rainforests technically do not have dry or wet seasons, since their rainfall is equally distributed through the year.<ref name="Hyde">{{cite web|author=Elisabeth M. Benders-Hyde|year=2003|url=http://www.blueplanetbiomes.org/climate.htm|title=World Climates|publisher=Blue Planet Biomes|access-date=27 December 2008|url-status=live|archive-url=https://web.archive.org/web/20081217015636/http://www.blueplanetbiomes.org/climate.htm|archive-date=17 December 2008}}</ref> Some areas with pronounced rainy seasons will see a break in rainfall mid-season when the [[Intertropical Convergence Zone]] or [[monsoon trough]] move poleward of their ___location during the middle of the warm season.<ref name="JS" /> When the wet season occurs during the warm season, or [[summer]], rain falls mainly during the late afternoon and early evening hours. The wet season is a time when both [[air quality]]<ref>{{cite thesis|author=Mei Zheng|year=2000|url=http://digitalcommons.uri.edu/dissertations/AAI9989458/|title=The sources and characteristics of atmospheric particulates during the wet and dry seasons in Hong Kong|type=PhD dissertation|pages=1–378|publisher=[[University of Rhode Island]]|access-date=27 December 2008|url-status=live|archive-url=https://web.archive.org/web/20090217060038/http://digitalcommons.uri.edu/dissertations/AAI9989458/|archive-date=17 February 2009|bibcode=2000PhDT........13Z |id={{ProQuest|304619312}} }}</ref> and [[freshwater]] quality improves.<ref>{{cite journal|author1=S. I. Efe|author2=F. E. Ogban|author3=M. J. Horsfall|author4=E. E. Akporhonor|year=2005|url=https://tspace.library.utoronto.ca/bitstream/1807/6445/1/ja05036.pdf|title=Seasonal Variations of Physico-chemical Characteristics in Water Resources Quality in Western Niger Delta Region, Nigeria|journal=Journal of Applied Scientific Environmental Management|access-date=27 December 2008|issn=1119-8362|volume=9|pages=191–195|issue=1|url-status=live|archive-url=https://web.archive.org/web/20090205200137/https://tspace.library.utoronto.ca/bitstream/1807/6445/1/ja05036.pdf|archive-date=5 February 2009}}</ref><ref>{{cite book|author1=C. D. Haynes |author2=M. G. Ridpath |author3=M. A. J. Williams |year=1991|url=https://books.google.com/books?id=ZhvtSmJYuN4C&pg=PA91|title=Monsoonal Australia|publisher=Taylor & Francis|page=90|isbn=978-90-6191-638-3}}</ref>
[[Tropical cyclone]]s, a source of very heavy rainfall, consist of large air masses several hundred miles across with low pressure at the centre and with winds blowing inward towards the centre in either a clockwise direction (southern hemisphere) or counterclockwise (northern hemisphere).<ref>{{cite web|author=Chris Landsea|year=2007|url=http://www.aoml.noaa.gov/hrd/tcfaq/D3.html|title=Subject: D3) Why do tropical cyclones' winds rotate counter-clockwise (clockwise) in the Northern (Southern) Hemisphere?|publisher=[[National Hurricane Center]]|access-date=2 January 2009|url-status=live|archive-url=https://web.archive.org/web/20090106113522/http://www.aoml.noaa.gov/hrd/tcfaq/D3.html|archive-date=6 January 2009|author-link=Chris Landsea}}</ref> Although [[cyclone]]s can take an enormous toll in lives and personal property, they may be important factors in the precipitation regimes of places they impact, as they may bring much-needed precipitation to otherwise dry regions.<ref name="2005 EPac outlook">{{cite web|author=Climate Prediction Center|year=2005|url=http://www.cpc.ncep.noaa.gov/products/Epac_hurr/Epac_hurricane.html|title=2005 Tropical Eastern North Pacific Hurricane Outlook|publisher=[[National Oceanic and Atmospheric Administration]]|access-date=2 May 2006|url-status=live|archive-url=https://web.archive.org/web/20090614024616/http://www.cpc.ncep.noaa.gov/products/Epac_hurr/Epac_hurricane.html|archive-date=14 June 2009|author-link=Climate Prediction Center}}</ref> Areas in their path can receive a year's worth of rainfall from a tropical cyclone passage.<ref>{{cite news|author=Jack Williams|url=https://www.usatoday.com/weather/whhcalif.htm|title=Background: California's tropical storms|work=[[USA Today]]|access-date=7 February 2009|date=17 May 2005|url-status=live|archive-url=https://web.archive.org/web/20090226172558/http://www.usatoday.com/weather/whhcalif.htm|archive-date=26 February 2009}}</ref>
===Human influence===
[[File:Change in Average Temperature With Fahrenheit.svg|thumb|upright=1.25|alt=World map of temperature distribution shows the northern hemisphere was warmer than the southern hemisphere during the periods compared.|Surface air temperature change over the past 50 years<ref>{{Cite web |title=GISS Surface Temperature Analysis (v4) |url=https://data.giss.nasa.gov/gistemp/maps/index_v4.html |access-date=12 January 2024 |website=NASA}}</ref>]]
{{See also|Effects of climate change|Effects of climate change on the water cycle|Urban heat island}}
The fine particulate matter produced by car exhaust and other human sources of pollution forms [[cloud condensation nuclei]] leads to the production of clouds and increases the likelihood of rain. As commuters and commercial traffic cause pollution to build up over the course of the week, the likelihood of rain increases: it peaks by Saturday, after five days of weekday pollution has been built up. In heavily populated areas that are near the coast, such as the United States' [[East Coast of the United States|Eastern Seaboard]], the effect can be dramatic: there is a 22% higher chance of rain on Saturdays than on Mondays.<ref>{{cite journal|date=6 August 1998|author1=R. S. Cerveny |author2=R. C. Balling |name-list-style=amp |title=Weekly cycles of air pollutants, precipitation and tropical cyclones in the coastal NW Atlantic region|journal=Nature|volume=394|pages=561–563|doi=10.1038/29043|issue=6693|bibcode = 1998Natur.394..561C |s2cid=204999292 }}</ref> The urban heat island effect warms cities {{convert|0.6|to|5.6|C|F}} above surrounding suburbs and rural areas. This extra heat leads to greater upward motion, which can induce additional shower and thunderstorm activity. Rainfall rates downwind of cities are increased between 48% and 116%. Partly as a result of this warming, monthly rainfall is about 28% greater between {{convert|20|and|40|mi|km|abbr=on|order=flip}} downwind of cities, compared with upwind.<ref>{{cite news | title=Spain goes hi-tech to beat drought | author=Dale Fuchs | work=The Guardian | date=28 June 2005 | url=https://www.theguardian.com/weather/Story/0,2763,1516375,00.html | access-date=2 August 2007 | ___location=London | url-status=live | archive-url=https://web.archive.org/web/20071104170020/http://www.guardian.co.uk/weather/Story/0%2C2763%2C1516375%2C00.html | archive-date=4 November 2007 }}</ref> Some cities induce a total precipitation increase of 51%.<ref>{{cite web|url=http://www.gsfc.nasa.gov/topstory/20020613urbanrain.html|title=NASA Satellite Confirms Urban Heat Islands Increase Rainfall Around Cities|author=Goddard Space Flight Center|publisher=[[National Aeronautics and Space Administration]]|date=18 June 2002|access-date=17 July 2009 |archive-url = https://web.archive.org/web/20080612173654/http://www.gsfc.nasa.gov/topstory/20020613urbanrain.html |archive-date = 12 June 2008|author-link=Goddard Space Flight Center}}</ref>
Increasing temperatures tend to increase evaporation which can lead to more precipitation. Precipitation generally increased over land north of 30°N from 1900 through 2005 but has declined over the tropics since the 1970s. Globally there has been no statistically significant overall trend in precipitation over the past century, although trends have varied widely by region and over time. Eastern portions of North and South America, northern Europe, and northern and central Asia have become wetter. The Sahel, the Mediterranean, southern Africa and parts of southern Asia have become drier. There has been an increase in the number of heavy precipitation events over many areas during the past century, as well as an increase since the 1970s in the prevalence of droughts—especially in the tropics and subtropics. Changes in precipitation and evaporation over the oceans are suggested by the decreased salinity of mid- and high-latitude waters (implying more precipitation), along with increased salinity in lower latitudes (implying less precipitation and/or more evaporation). Over the contiguous United States, total annual precipitation increased at an average rate of 6.1 percent since 1900, with the greatest increases within the East North Central climate region (11.6 percent per century) and the South (11.1 percent). Hawaii was the only region to show a decrease (−9.25 percent).<ref>{{cite web|url=http://www.epa.gov/climatechange/science/recentpsc.html|title=Precipitation and Storm Changes|author=Climate Change Division|publisher=[[United States Environmental Protection Agency]]|date=17 December 2008|access-date=17 July 2009|url-status=dead|archive-url=https://web.archive.org/web/20090718012707/http://epa.gov/climatechange/science/recentpsc.html|archive-date=18 July 2009}}</ref>
Analysis of 65 years of United States of America rainfall records show the lower 48 states have an increase in heavy downpours since 1950. The largest increases are in the Northeast and Midwest, which in the past decade, have seen 31 and 16 percent more heavy downpours compared to the 1950s. [[Rhode Island]] is the state with the largest increase, 104%. [[McAllen, Texas]] is the city with the largest increase, 700%. Heavy downpour in the analysis are the days where total precipitation exceeded the top one percent of all rain and snow days during the years 1950–2014.<ref>{{Cite web|title = Heaviest Downpours Rise across the U.S|url = http://www.scientificamerican.com/article/heaviest-downpours-rise-across-the-u-s|access-date = 28 May 2015|first = Climate|last = Central|website = [[Scientific American]]|url-status=live|archive-url = https://web.archive.org/web/20150528101535/http://www.scientificamerican.com/article/heaviest-downpours-rise-across-the-u-s/|archive-date = 28 May 2015}}</ref><ref>{{Cite web|title = Across U.S., Heaviest Downpours On The Rise {{!}} Climate Central|url = http://www.climatecentral.org/news/across-u.s.-heaviest-downpours-on-the-rise-18989|website = www.climatecentral.org|access-date = 28 May 2015|url-status=live|archive-url = https://web.archive.org/web/20150528061946/http://www.climatecentral.org/news/across-u.s.-heaviest-downpours-on-the-rise-18989|archive-date = 28 May 2015}}</ref>
The most successful attempts at influencing weather involve [[cloud seeding]], which include techniques used to increase [[snow|winter precipitation]] over mountains and suppress [[hail]].<ref name="AMSmod">{{cite web|url=http://www.ametsoc.org/policy/wxmod98.html |author=American Meteorological Society |title=Planned and Inadvertent Weather Modification |date=2 October 1998 |access-date=31 January 2010 |archive-url=https://web.archive.org/web/20100612213920/http://ametsoc.org/policy/wxmod98.html |archive-date=12 June 2010 }}</ref>
==Characteristics==
===Patterns===
[[File:Sturmfront auf Doppler-Radar-Schirm.jpg|thumb|Band of thunderstorms seen on a [[weather radar]] display]]
{{Main|Rainband}}
[[Rainband]]s are cloud and precipitation areas which are significantly elongated. Rainbands can be [[Stratus cloud|stratiform]] or [[atmospheric convection|convective]],<ref>Glossary of Meteorology (2009). [http://amsglossary.allenpress.com/glossary/search?p=1&query=rainband&submit=Search Rainband.] {{webarchive|url=https://web.archive.org/web/20110606102457/http://amsglossary.allenpress.com/glossary/search?p=1&query=rainband&submit=Search |date=6 June 2011 }} Retrieved on 24 December 2008.</ref> and are generated by differences in temperature. When noted on [[weather radar]] imagery, this precipitation elongation is referred to as banded structure.<ref>Glossary of Meteorology (2009). [http://amsglossary.allenpress.com/glossary/search?id=banded-structure1 Banded structure.] {{webarchive|url=https://web.archive.org/web/20110606102630/http://amsglossary.allenpress.com/glossary/search?id=banded-structure1 |date=6 June 2011 }} Retrieved on 24 December 2008.</ref> Rainbands in advance of warm [[occluded front]]s and [[warm front]]s are associated with weak upward motion,<ref>Owen Hertzman (1988). [http://adsabs.harvard.edu/abs/1988PhDT.......110H Three-Dimensional Kinematics of Rainbands in Midlatitude Cyclones.] Retrieved on 24 December 2008</ref> and tend to be wide and stratiform in nature.<ref>{{cite book|author=Yuh-Lang Lin|title=Mesoscale Dynamics|url=https://books.google.com/books?id=4KXtnQ3bDeEC&pg=PA405|year=2007|publisher=Cambridge University Press|isbn=978-0-521-80875-0|page=405}}</ref>
Rainbands spawned near and ahead of [[cold front]]s can be [[squall line]]s which are able to produce [[tornado]]es.<ref>Glossary of Meteorology (2009). [http://amsglossary.allenpress.com/glossary/search?id=prefrontal-squall-line1 Prefrontal squall line.] {{webarchive|url=https://web.archive.org/web/20070817224959/http://amsglossary.allenpress.com/glossary/search?id=prefrontal-squall-line1 |date=17 August 2007 }} Retrieved on 24 December 2008.</ref> Rainbands associated with cold fronts can be warped by mountain barriers perpendicular to the front's orientation due to the formation of a low-level [[barrier jet]].<ref>J. D. Doyle (1997). [http://cat.inist.fr/?aModele=afficheN&cpsidt=2721180 The influence of mesoscale orography on a coastal jet and rainband.] {{webarchive|url=https://web.archive.org/web/20120106231443/http://cat.inist.fr/?aModele=afficheN&cpsidt=2721180 |date=6 January 2012 }} Retrieved on 25 December 2008.</ref> Bands of thunderstorms can form with [[sea breeze]] and [[land breeze]] boundaries if enough moisture is present. If sea breeze rainbands become active enough just ahead of a cold front, they can mask the ___location of the cold front itself.<ref>A. Rodin (1995). [http://cat.inist.fr/?aModele=afficheN&cpsidt=3570629 Interaction of a cold front with a sea-breeze front numerical simulations.] {{webarchive|url=https://web.archive.org/web/20110909094659/http://cat.inist.fr/?aModele=afficheN&cpsidt=3570629 |date=9 September 2011 }} Retrieved on 25 December 2008.</ref>
Once a cyclone occludes an [[occluded front]] (a trough of warm air aloft) will be caused by strong southerly winds on its eastern periphery rotating aloft around its northeast, and ultimately northwestern, periphery (also termed the warm conveyor belt), forcing a surface trough to continue into the cold sector on a similar curve to the occluded front. The front creates the portion of an occluded cyclone known as its ''comma head'', due to the [[comma (punctuation)|comma]]-like shape of the mid-tropospheric cloudiness that accompanies the feature. It can also be the focus of locally heavy precipitation, with thunderstorms possible if the atmosphere along the front is unstable enough for convection.<ref name="TROW">{{cite web
| title = What is a TROWAL? via the Internet Wayback Machine
| author = St. Louis University
| date = 4 August 2003
| url = http://www.eas.slu.edu/CIPS/Presentations/Conferences/NWA2002/Snow_NWA_02/tsld003.htm
| access-date = 2 November 2006 |archive-url = https://web.archive.org/web/20060916052440/http://www.eas.slu.edu/CIPS/Presentations/Conferences/NWA2002/Snow_NWA_02/tsld003.htm |archive-date = 16 September 2006| author-link = St. Louis University
}}</ref> Banding within the comma head precipitation pattern of an [[extratropical cyclone]] can yield significant amounts of rain.<ref>David R. Novak, Lance F. Bosart, Daniel Keyser, and Jeff S. Waldstreicher (2002). [http://cstar.cestm.albany.edu/CAP_Projects/Project4/Banded%20Precip/novakWAF.pdf A Climatological and composite study of cold season banded precipitation in the Northeast United States.] {{webarchive|url=https://web.archive.org/web/20110719134657/http://cstar.cestm.albany.edu/CAP_Projects/Project4/Banded%20Precip/novakWAF.pdf |date=19 July 2011 }} Retrieved on 26 December 2008.</ref> Behind extratropical cyclones during fall and winter, rainbands can form downwind of relative warm bodies of water such as the [[Great Lakes]]. Downwind of islands, bands of showers and thunderstorms can develop due to low-level wind convergence downwind of the island edges. Offshore [[California]], this has been noted in the wake of cold fronts.<ref>Ivory J. Small (1999). [http://www.wrh.noaa.gov/wrh/99TAs/9918/index.html An observation study of island effect bands: precipitation producers in Southern California.] {{webarchive|url=https://web.archive.org/web/20120306040459/http://www.wrh.noaa.gov/wrh/99TAs/9918/index.html |date=6 March 2012 }} Retrieved on 26 December 2008.</ref>
Rainbands within tropical cyclones are curved in orientation. Tropical cyclone rainbands contain showers and thunderstorms that, together with the eyewall and the eye, constitute a [[tropical cyclone|hurricane or tropical storm]]. The extent of rainbands around a tropical cyclone can help determine the cyclone's intensity.<ref name="ODT">[[University of Wisconsin–Madison]] (1998).[http://cimss.ssec.wisc.edu/tropic/research/products/dvorak/odt.html Objective Dvorak Technique.] {{webarchive|url=https://web.archive.org/web/20060610051639/http://cimss.ssec.wisc.edu/tropic/research/products/dvorak/odt.html |date=10 June 2006 }} Retrieved on 29 May 2006.</ref>
===Acidity===
[[File:Origins of acid rain.svg|thumb|upright=1.25|Sources of acid rain]]
{{See also|Acid rain}}
The phrase ''acid rain'' was first used by Scottish chemist Robert Augus Smith in 1852.<ref>Encyclopædia Britannica</ref> The [[pH]] of rain varies, especially due to its origin. On America's East Coast, rain that is derived from the Atlantic Ocean typically has a pH of 5.0–5.6; rain that comes across the continental from the west has a pH of 3.8–4.8; and local thunderstorms can have a pH as low as 2.0.<ref>{{Cite journal|title=Effect of storm type on rainwater composition in southeastern North Carolina|journal=Environmental Science & Technology|volume=22|issue = 1|pages=41–46|author=Joan D. Willey|date=January 1988|doi=10.1021/es00166a003|pmid=22195508|last2=Bennett|last3=Williams|last4=Denne|last5=Kornegay|last6=Perlotto|last7=Moore|bibcode=1988EnST...22...41W}}</ref> Rain becomes acidic primarily due to the presence of two strong acids, [[sulfuric acid]] (H<sub>2</sub>SO<sub>4</sub>) and [[nitric acid]] (HNO<sub>3</sub>). Sulfuric acid is derived from natural sources such as volcanoes, and wetlands (sulfate-reducing bacteria); and anthropogenic sources such as the combustion of [[fossil fuels]], and mining where H<sub>2</sub>S is present. Nitric acid is produced by natural sources such as lightning, soil bacteria, and natural fires; while also produced anthropogenically by the combustion of fossil fuels and from power plants. In the past 20 years, the concentrations of nitric and sulfuric acid has decreased in presence of rainwater, which may be due to the significant increase in ammonium (most likely as ammonia from livestock production), which acts as a [[buffer solution|buffer]] in acid rain and raises the pH.<ref>{{Cite journal|title=Changing Chemical Composition of Precipitation in Wilmington, North Carolina, U.S.A.: Implications for the Continental U.S.A|journal=Environmental Science & Technology|volume=40|issue=18|pages=5675–5680|author=Joan D. Willey|date=19 August 2006|doi=10.1021/es060638w|last2=Kieber|last3=Avery|pmid=17007125|bibcode=2006EnST...40.5675W}}</ref>
===Köppen climate classification===
[[File:World Köppen Classification (with authors).svg|thumb|upright=1.75|Updated Köppen–Geiger climate map<ref>{{cite journal |author=Peel, M. C. |author2=Finlayson, B. L. |author3=McMahon, T. A. |year=2007 |title=Updated world map of the Köppen–Geiger climate classification |journal=Hydrology and Earth System Sciences |volume=11 |issue=5 | pages=1633–1644 |doi=10.5194/hess-11-1633-2007 |issn=1027-5606 |doi-access=free |bibcode=2007HESS...11.1633P}} ''(direct:[http://www.hydrol-earth-syst-sci.net/11/1633/2007/hess-11-1633-2007.pdf Final Revised Paper] {{webarchive|url=https://web.archive.org/web/20120203170339/http://www.hydrol-earth-syst-sci.net/11/1633/2007/hess-11-1633-2007.pdf |date=3 February 2012 }})''</ref>
{|
|- valign=top |
|
{{legend|#0000FE|[[equatorial climate|Af]]}}
{{legend|#0077FF|[[monsoon|Am]]}}
{{legend|#46A9FA|[[tropical savanna climate|Aw]]}}
| width=5 |
|
{{legend|#FE0000|[[desert climate|BWh]]}}
{{legend|#FE9695|[[desert climate|BWk]]}}
{{legend|#F5A301|[[semi-arid climate|BSh]]}}
{{legend|#FFDB63|[[semi-arid climate|BSk]]}}
| width=5 |
|
{{legend|#FFFF00|[[mediterranean climate|Csa]]}}
{{legend|#C6C700|[[mediterranean climate|Csb]]}}
| width=5 |
|
{{legend|#96FF96|[[humid subtropical climate|Cwa]]}}
{{legend|#63C764|[[oceanic climate|Cwb]]}}
| width=5 |
|
{{legend|#C6FF4E|[[Humid subtropical climate|Cfa]]}}
{{legend|#66FF33|[[oceanic climate|Cfb]]}}
{{legend|#33C701|[[oceanic climate|Cfc]]}}
| width=5 |
|
{{legend|#FF00FE|[[continental climate|Dsa]]}}
{{legend|#C600C7|[[continental climate|Dsb]]}}
{{legend|#963295|[[continental climate|Dsc]]}}
{{legend|#966495|[[continental climate|Dsd]]}}
| width=5 |
|
{{legend|#ABB1FF|[[humid continental climate|Dwa]]}}
{{legend|#5A77DB|[[humid continental climate|Dwb]]}}
{{legend|#4C51B5|[[subarctic climate|Dwc]]}}
{{legend|#320087|[[subarctic climate|Dwd]]}}
| width=5 |
|
{{legend|#00FFFF|[[humid continental climate|Dfa]]}}
{{legend|#38C7FF|[[humid continental climate|Dfb]]}}
{{legend|#007E7D|[[subarctic climate|Dfc]]}}
{{legend|#00455E|[[subarctic climate|Dfd]]}}
| width=5 |
|
{{legend|#B2B2B2|[[tundra climate|ET]]}}
{{legend|#686868|[[ice cap climate|EF]]}}
|}
]]
{{Main|Köppen climate classification}}
The Köppen classification depends on average monthly values of temperature and precipitation. The most commonly used form of the Köppen classification has five primary types labeled A through E. Specifically, the primary types are A, tropical; B, dry; C, mild mid-latitude; D, cold mid-latitude; and E, polar. The five primary classifications can be further divided into secondary classifications such as [[rain forest]], [[monsoon]], [[tropical savanna]], [[humid subtropical]], [[humid continental]], [[oceanic climate]], [[Mediterranean climate]], [[steppe]], [[subarctic climate]], [[tundra]], [[polar ice cap]], and [[desert]].<ref>{{Cite journal |last1=Kottek |first1=Markus |last2=Grieser |first2=Jürgen |last3=Beck |first3=Christoph |last4=Rudolf |first4=Bruno |last5=Rubel |first5=Franz |date=2006-07-10 |title=World Map of the Köppen-Geiger climate classification updated |url=http://www.schweizerbart.de/papers/metz/detail/15/55034/World_Map_of_the_Koppen_Geiger_climate_classificat?af=crossref |journal=Meteorologische Zeitschrift |language=en |volume=15 |issue=3 |pages=259–263 |doi=10.1127/0941-2948/2006/0130 |bibcode=2006MetZe..15..259K |issn=0941-2948}}</ref>
Rain forests are characterized by high rainfall, with definitions setting minimum normal annual rainfall between {{convert|1750|and|2000|mm|in|abbr=on}}.<ref>{{cite web|author=Susan Woodward |url=http://www.radford.edu/~swoodwar/CLASSES/GEOG235/biomes/rainforest/rainfrst.html |title=Tropical Broadleaf Evergreen Forest: The Rainforest |date=29 October 1997 |access-date=14 March 2008 |publisher=[[Radford University]] |archive-url=https://web.archive.org/web/20080225054655/http://www.radford.edu/~swoodwar/CLASSES/GEOG235/biomes/rainforest/rainfrst.html |archive-date=25 February 2008 }}</ref> A tropical savanna is a [[grassland]] [[biome]] located in [[semi-arid]] to [[humid|semi-humid]] climate regions of [[subtropical]] and [[tropical]] [[latitudes]], with rainfall between {{convert|750|and|1270|mm|in|abbr=on}} a year. They are widespread on Africa, and are also found in India, the northern parts of South America, [[Malaysia]], and Australia.<ref name="SAVWOOD">{{cite web|author=Susan Woodward |url=http://www.radford.edu/~swoodwar/CLASSES/GEOG235/biomes/savanna/savanna.html |title=Tropical Savannas |date=2 February 2005 |access-date=16 March 2008 |publisher=Radford University |archive-url=https://web.archive.org/web/20080225082154/http://www.radford.edu/~swoodwar/CLASSES/GEOG235/biomes/savanna/savanna.html |archive-date=25 February 2008 }}</ref> The humid subtropical climate zone is where winter rainfall is associated with large [[storm]]s that the [[westerlies]] steer from west to east. Most summer rainfall occurs during thunderstorms and from occasional tropical cyclones.<ref>{{cite encyclopedia | title = Humid subtropical climate | encyclopedia = [[Encyclopædia Britannica]] | year = 2008 | url = http://www.britannica.com/eb/article-53358/climate | access-date = 14 May 2008 | url-status=live | archive-url = https://web.archive.org/web/20080511070755/http://www.britannica.com/eb/article-53358/climate | archive-date = 11 May 2008 }}</ref> Humid subtropical climates lie on the east side continents, roughly between [[latitude]]s 20° and 40° degrees away from the equator.<ref>{{cite web|author=Michael Ritter |url=http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/climate_systems/humid_subtropical.html |date=24 December 2008 |publisher=University of Wisconsin–Stevens Point |title=Humid Subtropical Climate |access-date=16 March 2008 |archive-url=https://web.archive.org/web/20081014093644/http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/climate_systems/humid_subtropical.html |archive-date=14 October 2008 }}</ref>
An oceanic (or maritime) climate is typically found along the west coasts at the middle latitudes of all the world's continents, bordering cool oceans, as well as southeastern Australia, and is accompanied by plentiful precipitation year-round.<ref>{{cite book|author=Lauren Springer Ogden|title=Plant-Driven Design|page=[https://archive.org/details/plantdrivendesig0000ogde/page/78 78]|isbn=978-0-88192-877-8|publisher=Timber Press|year=2008|url=https://archive.org/details/plantdrivendesig0000ogde/page/78}}</ref> The Mediterranean climate regime resembles the climate of the lands in the [[Mediterranean Basin]], parts of western North America, parts of [[Western Australia|Western]] and [[South Australia]], in southwestern [[South Africa]] and in parts of central [[Chile]]. The climate is characterized by hot, dry summers and cool, wet winters.<ref>{{cite web|author=Michael Ritter |url=http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/climate_systems/mediterranean.html |title=Mediterranean or Dry Summer Subtropical Climate |access-date=17 July 2009 |date=24 December 2008 |publisher=[[University of Wisconsin–Stevens Point]] |archive-url=https://web.archive.org/web/20090805040919/http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/climate_systems/mediterranean.html |archive-date=5 August 2009 }}</ref> A steppe is a dry [[grassland]].<ref>{{cite web|author1=Brynn Schaffner|author2=Kenneth Robinson|name-list-style=amp|url=http://www.blueplanetbiomes.org/steppe_climate_page.htm|title=Steppe Climate|date=6 June 2003|access-date=15 April 2008|publisher=West Tisbury Elementary School|archive-url=https://web.archive.org/web/20080422233231/http://www.blueplanetbiomes.org/steppe_climate_page.htm|archive-date=22 April 2008}}</ref> Subarctic climates are cold with continuous [[permafrost]] and little precipitation.<ref name="subritter">{{cite web|author=Michael Ritter |url=http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/climate_systems/subarctic.html |title=Subarctic Climate |access-date=16 April 2008 |publisher=[[University of Wisconsin–Stevens Point]] |date=24 December 2008 |archive-url=https://web.archive.org/web/20080525080242/http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/climate_systems/subarctic.html |archive-date=25 May 2008 }}</ref>
===Pollution and composition===
Aside from contamination of rainwater by [[Sulfur(IV) oxide|sulfuric]] and [[nitric oxides]], which produces acid rain, various pollutants from industry and household wastes can end up in rainwater, causing detrimental effects on aquatic and human life. Pollutants from solid waste, leaking vehicles and machinery, fertilizers and other potentially hazardous substances enter water sources directly through dumping or as [[surface runoff]] following heavy rain.<ref>{{Cite journal |last=Saxena |first=Vivek |date=2025 |title=Water Quality, Air Pollution, and Climate Change: Investigating the Environmental Impacts of Industrialization and Urbanization |url=https://link.springer.com/10.1007/s11270-024-07702-4 |journal=Water, Air, & Soil Pollution |language=en |volume=236 |issue=2 |article-number=73 |doi=10.1007/s11270-024-07702-4 |bibcode=2025WASP..236...73S |issn=0049-6979|url-access=subscription }}</ref> One classification of pollutants of particular note is [[Perfluoroalkyl acid|perfluoroalkyl substances]], synthetic chemical compounds used in a wide variety of consumer products.<ref name="Evidence">{{cite journal |display-authors=6 |vauthors=Munoz G, Budzinski H, Babut M, Drouineau H, Lauzent M, Menach KL, Lobry J, Selleslagh J, Simonnet-Laprade C, Labadie P |date=August 2017 |title=Evidence for the Trophic Transfer of Perfluoroalkylated Substances in a Temperate Macrotidal Estuary |url=https://hal.archives-ouvertes.fr/hal-02067250/file/Main%20text_R1_2017-06-27.pdf |journal=Environmental Science & Technology |volume=51 |issue=15 |pages=8450–8459 |bibcode=2017EnST...51.8450M |doi=10.1021/acs.est.7b02399 |pmid=28679050}}</ref> Rain has the potential to dissolve and transport different compounds, including the aforementioned toxic substances, with certain ions such as [[Calcium ion|calcium]] and [[bicarbonate]] appearing frequently, in more acidic rainwater.<ref>{{Cite journal |last1=Ongetta |first1=Stephan |last2=Mohan Viswanathan |first2=Prasanna |last3=Mishra |first3=Anshuman |last4=Sabarathinam |first4=Chidambaram |date=2025-05-17 |title=A Multiproxy Analysis of Rainwater Chemistry and Moisture Sources in Borneo |journal=Earth Systems and Environment |language=en |doi=10.1007/s41748-025-00653-8 |bibcode=2025ESE...tmp..112O |issn=2509-9434|doi-access=free }}</ref> However, the composition of rainwater at any given time and place is highly variable based on the ongoing manufacturing, farming, and waste-producing activities.<ref>{{Cite journal |last1=Gajewska |first1=Magdalena |last2=Fitobór |first2=Karolina |last3=Artichowicz |first3=Wojciech |last4=Ulańczyk |first4=Rafał |last5=Kida |first5=Małgorzata |last6=Kołecka |first6=Katarzyna |date=2024-08-05 |title=Occurrence of specific pollutants in a mixture of sewage and rainwater from an urbanized area |journal=Scientific Reports |language=en |volume=14 |issue=1 |pages=18119 |doi=10.1038/s41598-024-69099-8 |pmid=39103480 |issn=2045-2322 |pmc=11300779 |bibcode=2024NatSR..1418119G }}</ref>{{Excerpt|Per- and polyfluoroalkyl substances|Prevalence in rain, soil, water bodies, and air}}
==Measurement==
{{See also|Precipitation#Rate}}
===Gauges===
{{See also|Rain gauge|Disdrometer|Snow gauge}}
[[File:250mm Rain Gauge.jpg|thumb|upright=0.55|left|Standard rain gauge]]
Rain rate is measured in units of length per unit time, typically in millimeters per hour,<ref>{{Cite book|chapter-url=https://library.wmo.int/viewer/68695/?offset=3#page=246|title=Guide to Meteorological Instruments and Methods of Observation (WMO-No. 8) Vol. I Measurement of Meteorological Variables|publisher=[[World Meteorological Organization]]|year=2024|edition=Eighth|pages=224|chapter=6. Measurement of Precipitation}}</ref> or in countries where [[imperial units]] are more common, inches per hour.<ref>{{cite web |url=http://training.fema.gov/EMIWeb/edu/docs/fem/Chapter%205%20-%20Principal%20Hazards%20in%20U.S.doc |title=Chapter 5 – Principal Hazards in U.S.doc |page=128 |archive-url=https://web.archive.org/web/20130227203957/http://training.fema.gov/emiweb/edu/docs/fem/Chapter%205%20-%20Principal%20Hazards%20in%20U.S.doc |archive-date=27 February 2013 |access-date=17 October 2015 }}</ref> The "length", or more accurately, "depth" being measured is the depth of rain water that would accumulate on a flat, horizontal and impermeable surface during a given amount of time, typically an hour.<ref>{{cite web|url=http://www.newton.dep.anl.gov/askasci/gen99/gen99115.htm|title=Classroom Resources – Argonne National Laboratory|access-date=23 December 2016|url-status=live|archive-url=https://web.archive.org/web/20150226035934/http://www.newton.dep.anl.gov/askasci/gen99/gen99115.htm|archive-date=26 February 2015}}</ref> This is [[Dimensional analysis|dimensionally]] equivalent to volume of water per unit area: one millimeter of rainfall is the equivalent of one liter of water per square meter.<ref>{{cite web |url=http://www.fao.org/docrep/r4082e/r4082e05.htm |title=FAO.org |publisher=FAO.org |access-date=26 December 2011 |url-status=live |archive-url=https://web.archive.org/web/20120126041141/http://www.fao.org/docrep/r4082e/r4082e05.htm |archive-date=26 January 2012 }}</ref> This measurement is done with a [[rain gauge|gauge]]. A cylindrical can with straight sides is the most inexpensive and simple used that can be made and left out in the open, but its accuracy will depend on what ruler is used to measure the rain with.<ref>{{cite web|author=Discovery School|year=2009|url=http://school.discovery.com/lessonplans/activities/weatherstation/itsrainingitspouring.html|title=Build Your Own Weather Station|publisher=Discovery Education|access-date=2 January 2009|archive-url=https://web.archive.org/web/20080828214157/http://school.discovery.com/lessonplans/activities/weatherstation/itsrainingitspouring.html <!--Added by H3llBot-->|archive-date=28 August 2008}}</ref> Meteorologists have a standard type of gauge for both rainfall or snowfall with an inner cylinder and an outer cylinder that adds to the volume of the full inner cylinder.<ref>{{Cite web |last=Lehmann |first=Chris |date=2009 |title=2000 Reminders-4Q |url=http://nadp.sws.uiuc.edu/cal/2000_reminders-4thQ.htm |archive-url=https://web.archive.org/web/20100615115408/http://nadp.sws.uiuc.edu/cal/2000_reminders-4thQ.htm |archive-date=15 June 2010 |website=Central Analytical Laboratory}}</ref> Other types of gauges include the popular wedge gauge (the cheapest rain gauge and most fragile), the tipping bucket rain gauge, and the weighing rain gauge.<ref>{{cite web|author=National Weather Service|year=2009|url=http://www.weather.gov/glossary/index.php?letter=w|title=Glossary: W|access-date=1 January 2009|url-status=live|archive-url=https://web.archive.org/web/20081218124142/http://www.weather.gov/glossary/index.php?letter=w|archive-date=18 December 2008|author-link=National Weather Service}}</ref>
When a precipitation measurement is made, various networks exist across the United States and elsewhere where rainfall measurements can be submitted through the Internet, such as [[Community Collaborative Rain, Hail and Snow network|CoCoRAHS]] or GLOBE.<ref>{{cite web|url=http://cocorahs.org|title=Community Collaborative Rain, Hail & Snow Network Main Page|publisher=Colorado Climate Center|year=2009|access-date=2 January 2009|url-status=live|archive-url=https://web.archive.org/web/20090106125523/http://cocorahs.org/|archive-date=6 January 2009}}</ref><ref>{{cite web|title=Global Learning and Observations to Benefit the Environment Program|url=http://www.globe.gov/fsl/welcome/welcomeobject.pl|author=The Globe Program|year=2009|access-date=2 January 2009|archive-url=https://web.archive.org/web/20060819010615/http://www.globe.gov/fsl/welcome/welcomeobject.pl|archive-date=19 August 2006}}</ref> If a network is not available in the area where one lives, the nearest local weather or met office will likely be interested in the measurement.<ref>{{cite web|author=National Weather Service|year=2009|url=http://www.nws.noaa.gov|title=NOAA's National Weather Service Main Page|access-date=1 January 2009|url-status=live|archive-url=https://web.archive.org/web/20090101124443/http://nws.noaa.gov/|archive-date=1 January 2009|author-link=National Weather Service}}</ref>
===Remote sensing===
{{See also|Weather radar}}
[[File:Radar-accumulations eng.png|thumb|Twenty-four-hour rainfall accumulation on the Val d'Irène radar in Eastern Canada. Zones without data in the east and southwest are caused by beam blocking from mountains (source: Environment Canada).]]
One of the main uses of weather radar is to be able to assess the amount of precipitations fallen over large basins for [[hydrology|hydrological]] purposes.<ref>{{Cite book|author1=Kang-Tsung Chang, Jr-Chuan Huang |author2=Shuh-Ji Kao |author3=Shou-Hao Chiang |title=Data Assimilation for Atmospheric, Oceanic and Hydrologic Applications |chapter=Radar Rainfall Estimates for Hydrologic and Landslide Modeling |name-list-style=amp |doi=10.1007/978-3-540-71056-1_6|isbn=978-3-540-71056-1|year=2009|pages=127–145}}</ref> For instance, river [[flood control]], sewer management and dam construction are all areas where planners use rainfall accumulation data. Radar-derived rainfall estimates complement surface station data which can be used for calibration. To produce radar accumulations, rain rates over a point are estimated by using the value of reflectivity data at individual grid points. A radar equation is then used, which is
<math display="block"> Z = A R^b ,</math>
where Z represents the radar reflectivity, R represents the rainfall rate, and A and b are constants.<ref>{{cite web|url=https://ecommons.library.cornell.edu/bitstream/1813/2115/1/pdfthesis.pdf|publisher=[[Cornell University]]|author=Eric Chay Ware|title=Corrections to Radar-Estimated Precipitation Using Observed Rain Gauge Data: A Thesis|date=August 2005|page=1|access-date=2 January 2010|url-status=live|archive-url=https://web.archive.org/web/20100726140335/http://ecommons.library.cornell.edu/bitstream/1813/2115/1/pdfthesis.pdf|archive-date=26 July 2010}}</ref>
Satellite-derived rainfall estimates use passive [[microwave]] instruments aboard [[polar orbit]]ing as well as [[geostationary orbit|geostationary]] [[weather satellite]]s to indirectly measure rainfall rates.<ref>{{cite web |url=http://www.isac.cnr.it/~ipwg/meetings/melbourne/papers/Mngadi.pdf |archive-url=https://www.webcitation.org/5nAoR7J6a?url=http://www.isac.cnr.it/~ipwg/meetings/melbourne/papers/Mngadi.pdf |archive-date=30 January 2010 |title=Southern Africa Satellite Derived Rainfall Estimates Validation |author1=Pearl Mngadi |author2=Petrus JM Visser |author3=Elizabeth Ebert |name-list-style=amp |page=1 |publisher=International Precipitation Working Group |date=October 2006 |access-date=5 January 2010 }}</ref> If one wants an accumulated rainfall over a time period, one has to add up all the accumulations from each grid box within the images during that time.
{{multiple image
| align = left
| direction = horizontal
| image1 = 1988 US Rain.ogv
| width1 = 300
| alt1 =
| caption1 = 1988 rain in the U.S. The heaviest rain is seen in reds and yellows.
| image2 = 1993 US Rain.ogv
| width2 = 300
| alt2 =
| caption2 = 1993 rain in the U.S.
}}
{{Clear}}
===Intensity===
[[File:Lluvia intensa.ogg|thumb|alt=Heavy rain in Zapopan|Heavy rain in [[Zapopan]]]]
{{listen
| filename = Heavy rain in Glenshaw, PA.ogg
| title = Heavy rain in Glenshaw, Pennsylvania
| description = The sound of heavy rainfall in a suburban neighborhood
}}
Rainfall intensity is classified according to the rate of precipitation, which depends on the considered time.<ref name=Monjo1>{{Cite journal|last=Monjo|first=R.|date=2016|title=Measure of rainfall time structure using the dimensionless n-index |journal=Climate Research|volume=67|issue=1|pages=71–86|doi=10.3354/cr01359|bibcode=2016ClRes..67...71M|doi-access=free}} [https://www.int-res.com/articles/cr_oa/c067p071.pdf (pdf)] {{webarchive|url=https://web.archive.org/web/20170106153819/https://www.int-res.com/articles/cr_oa/c067p071.pdf |date=6 January 2017 }}</ref> The following categories are used to classify rainfall intensity:
* Light rain – when the precipitation rate is less than {{convert|2.5|mm|in|abbr=on}} per hour
* Moderate rain – when the precipitation rate is between {{convert|2.5|and(-)|7.6|mm|in|abbr=on}} or {{convert|10|mm|in|abbr=on}} per hour<ref name="rainint"/><ref name="UKint">{{cite web
|page=6
|url=http://www.metoffice.gov.uk/media/pdf/4/1/No._03_-_Water_in_the_Atmosphere.pdf
|title=Fact Sheet No. 3: Water in the Atmosphere
|publisher=Crown Copyright
|date=August 2007
|author=Met Office
|access-date=12 May 2011
|archive-url=https://web.archive.org/web/20120114162401/http://www.metoffice.gov.uk/media/pdf/4/1/No._03_-_Water_in_the_Atmosphere.pdf
|archive-date=14 January 2012
}}</ref>
* Heavy rain – when the precipitation rate is greater than {{convert|7.6|mm|in|abbr=on}} per hour,<ref name="rainint">{{cite web|date=June 2000|url=http://amsglossary.allenpress.com/glossary/search?id=rain1|work=Glossary of Meteorology|title=Rain|publisher=[[American Meteorological Society]]|access-date=15 January 2010|archive-url=https://web.archive.org/web/20100725142506/http://amsglossary.allenpress.com/glossary/search?id=rain1|archive-date=25 July 2010}}</ref> or between {{convert|10|and(-)|50|mm|in|abbr=on}} per hour<ref name="UKint"/>
* Violent rain – when the precipitation rate is greater than {{convert|50|mm|in|abbr=on}} per hour<ref name="UKint"/>
The intensity can also be expressed by rainfall erosivity ''R-factor''<ref>{{cite journal | doi = 10.1016/j.scitotenv.2015.01.008 | pmid = 25622150 | volume=511 | title=Rainfall erosivity in Europe | journal=Science of the Total Environment | pages=801–814| year = 2015 | last1 = Panagos | first1 = Panos | last2 = Ballabio | first2 = Cristiano | last3 = Borrelli | first3 = Pasquale | last4 = Meusburger | first4 = Katrin | last5 = Klik | first5 = Andreas | last6 = Rousseva | first6 = Svetla | last7 = Tadić | first7 = Melita Perčec | last8 = Michaelides | first8 = Silas | last9 = Hrabalíková | first9 = Michaela | last10 = Olsen | first10 = Preben | last11 = Aalto | first11 = Juha | last12 = Lakatos | first12 = Mónika | last13 = Rymszewicz | first13 = Anna | last14 = Dumitrescu | first14 = Alexandru | last15 = Beguería | first15 = Santiago | last16 = Alewell | first16 = Christine | bibcode = 2015ScTEn.511..801P | doi-access = free | hdl = 10261/110151 | hdl-access = free }}</ref> or in terms of the rainfall time-structure ''n-index''.<ref name=Monjo1/>
{{clear}}
===Return period===
{{See also|100-year flood}}
The average time between occurrences of an event with a specified intensity and duration is called the [[return period]].<ref name=glossary>{{cite web|author=Glossary of Meteorology|year=2009|url=http://amsglossary.allenpress.com/glossary/search?id=return-period1|title=Return period|publisher=[[American Meteorological Society]]|access-date=2 January 2009|archive-url=https://web.archive.org/web/20061020151220/http://amsglossary.allenpress.com/glossary/search?id=return-period1|archive-date=20 October 2006}}</ref> The intensity of a storm can be predicted for any return period and storm duration, from charts based on historic data for the ___location.<ref>{{cite web|author=Glossary of Meteorology|year=2009|url=http://amsglossary.allenpress.com/glossary/search?p=1&query=return+period&submit=Search|title=Rainfall intensity return period|publisher=[[American Meteorological Society]]|access-date=2 January 2009|archive-url=https://web.archive.org/web/20110606085617/http://amsglossary.allenpress.com/glossary/search?p=1&query=return+period&submit=Search|archive-date=6 June 2011}}</ref> The return period is often expressed as an ''n''-year event. For instance, a 10-year storm describes a rare rainfall event occurring on average once every 10 years. The rainfall will be greater and the flooding will be worse than the worst storm expected in any single year. A 100-year storm describes an extremely rare rainfall event occurring on average once in a century. The rainfall will be extreme and flooding worse than a 10-year event. The probability of an event in any year is the inverse of the return period (assuming the probability remains the same for each year).<ref name=glossary/> For instance, a 10-year storm has a probability of occurring of 10 percent in any given year, and a 100-year storm occurs with a 1 percent probability in a year. As with all probability events, it is possible, though improbable, to have multiple 100-year storms in a single year.<ref>{{cite web|author=Boulder Area Sustainability Information Network|year=2005|url=http://bcn.boulder.co.us/basin/watershed/flood.html|title=What is a 100 year flood?|publisher=Boulder Community Network|access-date=2 January 2009|url-status=live|archive-url=https://web.archive.org/web/20090219212140/http://bcn.boulder.co.us/basin/watershed/flood.html|archive-date=19 February 2009}}</ref>
==Forecasting==
{{Main|Quantitative precipitation forecast}}
[[File:Rita5dayqpf.png|thumb|upright=1.25|Example of a five-day rainfall forecast from the [[Hydrometeorological Prediction Center]]]]
The Quantitative Precipitation Forecast (abbreviated QPF) is the expected amount of liquid precipitation accumulated over a specified time period over a specified area.<ref name="SERFC">{{cite web|author=Jack S. Bushong |year=1999 |url=http://cms.ce.gatech.edu/gwri/uploads/proceedings/1999/BushongJ-99.pdf |title=Quantitative Precipitation Forecast: Its Generation and Verification at the Southeast River Forecast Center |publisher=[[University of Georgia]] |access-date=31 December 2008 |archive-url=https://web.archive.org/web/20090205200117/http://cms.ce.gatech.edu/gwri/uploads/proceedings/1999/BushongJ-99.pdf |archive-date=5 February 2009 }}</ref> A QPF will be specified when a measurable precipitation type reaching a minimum threshold is forecast for any hour during a QPF valid period. Precipitation forecasts tend to be bound by synoptic hours such as 0000, 0600, 1200 and 1800 [[GMT]]. Terrain is considered in QPFs by use of topography or based upon climatological precipitation patterns from observations with fine detail.<ref>{{cite web|author=Daniel Weygand|year=2008|url=http://www.wrh.noaa.gov/wrh/talite0821.pdf|title=Optimizing Output From QPF Helper|publisher=[[National Weather Service]] Western Region|access-date=31 December 2008|archive-url=https://web.archive.org/web/20090205201644/http://www.wrh.noaa.gov/wrh/talite0821.pdf|archive-date=5 February 2009}}</ref> Starting in the mid to late 1990s, QPFs were used within hydrologic forecast models to simulate impact to rivers throughout the United States.<ref>{{cite web|author=Noreen O. Schwein|year=2009|url=http://ams.confex.com/ams/89annual/techprogram/paper_149707.htm|title=Optimization of quantitative precipitation forecast time horizons used in river forecasts|publisher=[[American Meteorological Society]]|access-date=31 December 2008|archive-url=https://web.archive.org/web/20110609174227/http://ams.confex.com/ams/89annual/techprogram/paper_149707.htm|archive-date=9 June 2011}}</ref>
[[Numerical weather prediction|Forecast models]] show significant sensitivity to humidity levels within the [[planetary boundary layer]], or in the lowest levels of the atmosphere, which decreases with height.<ref>{{cite journal |author=Christian Keil |author2=Andreas Röpnack |author3=George C. Craig |author4=Ulrich Schumann |url=http://www.agu.org/pubs/crossref/2008/2008GL033657.shtml|title=Sensitivity of quantitative precipitation forecast to height dependent changes in humidity|journal=Geophysical Research Letters|volume=35|doi=10.1029/2008GL033657|date=31 December 2008|pages=L09812|bibcode=2008GeoRL..35.9812K|issue=9|url-status=live|archive-url=https://web.archive.org/web/20110606060227/http://www.agu.org/pubs/crossref/2008/2008GL033657.shtml|archive-date=6 June 2011|doi-access=free}}</ref> QPF can be generated on a quantitative, forecasting amounts, or a qualitative, forecasting the probability of a specific amount, basis.<ref>{{cite journal |author1=Reggiani, P. |author2=Weerts, A. H. |title=Probabilistic Quantitative Precipitation Forecast for Flood Prediction: An Application |journal=Journal of Hydrometeorology |date=February 2008 |pages=76–95 |volume=9 |issue=1 |doi=10.1175/2007JHM858.1 |bibcode=2008JHyMe...9...76R|doi-access=free }}</ref> Radar imagery forecasting techniques show higher [[Forecast skill|skill]] than model forecasts within 6 to 7 hours of the time of the radar image. The forecasts can be verified through use of rain gauge measurements, weather radar estimates, or a combination of both. Various skill scores can be determined to measure the value of the rainfall forecast.<ref name="Canada">{{cite web|author=Charles Lin |year=2005 |url=http://www.actif-ec.net/Workshop2/Presentations/ACTIF_P_S1_02.pdf |title=Quantitative Precipitation Forecast (QPF) from Weather Prediction Models and Radar Nowcasts, and Atmospheric Hydrological Modelling for Flood Simulation |publisher=Achieving Technological Innovation in Flood Forecasting Project |access-date=1 January 2009 |archive-url=https://web.archive.org/web/20090205200121/http://www.actif-ec.net/Workshop2/Presentations/ACTIF_P_S1_02.pdf |archive-date=5 February 2009 }}</ref>
==Impact==
===Agricultural===
[[File:Heavy Rains in Southern Japan.gif|thumb|Rainfall estimates for southern Japan and the surrounding region from 20 to 27 July 2009]]
Precipitation, especially rain, has a dramatic effect on agriculture. All plants need at least some water to survive, therefore rain (being the most effective means of watering) is important to agriculture. While a regular rain pattern is usually vital to healthy plants, too much or too little rainfall can be harmful, even devastating to crops. [[Drought]] can kill crops and increase erosion,<ref>{{cite web|url=http://www.bom.gov.au/climate/drought/livedrought.shtml |title=Living With Drought |author=Bureau of Meteorology |publisher=Commonwealth of Australia |year=2010 |access-date=15 January 2010 |archive-url=https://web.archive.org/web/20070218192510/http://www.bom.gov.au/climate/drought/livedrought.shtml |archive-date=18 February 2007 |author-link=Bureau of Meteorology }}</ref> while overly wet weather can cause harmful [[fungus]] growth.<ref>{{cite web|url=http://agnewsarchive.tamu.edu/dailynews/stories/CROP/Jun0607a.htm |title=Texas Crop and Weather |date=6 June 2007 |author=Robert Burns |publisher=[[Texas A&M University]] |access-date=15 January 2010 |archive-url=https://web.archive.org/web/20100620134950/http://agnewsarchive.tamu.edu/dailynews/stories/CROP/Jun0607a.htm |archive-date=20 June 2010 }}</ref> Plants need varying amounts of rainfall to survive.<ref>{{Cite journal |last=C. |first=W. A. |date=1914 |editor-last=Briggs |editor-first=L. J. |editor2-last=Shantz |editor2-first=H. L. |title=The Water Requirement of Plants |url=https://www.jstor.org/stable/43477376 |journal=The Plant World |volume=17 |issue=3 |pages=76–78 |jstor=43477376 |issn=0096-8307}}</ref> For example, certain [[cactus|cacti]] require small amounts of water,<ref>{{cite web|url=http://www.sbs.utexas.edu/mauseth/researchoncacti/|title=Mauseth Research: Cacti|author=James D. Mauseth|publisher=University of Texas|date=7 July 2006|access-date=15 January 2010|url-status=live|archive-url=https://web.archive.org/web/20100527105209/http://www.sbs.utexas.edu/mauseth/ResearchOnCacti/|archive-date=27 May 2010}}</ref> while crops such as [[rice]] require thousands of liters of water to provide good yields and must be continuously [[Irrigation|irrigated]] in addition to normal watering through rainfall.<ref>{{Cite journal |last1=Zhao |first1=Xueyin |last2=Chen |first2=Mengting |last3=Xie |first3=Hua |last4=Luo |first4=Wanqi |last5=Wei |first5=Guangfei |last6=Zheng |first6=Shizong |last7=Wu |first7=Conglin |last8=Khan |first8=Shahbaz |last9=Cui |first9=Yuanlai |last10=Luo |first10=Yufeng |date=2023-04-30 |title=Analysis of irrigation demands of rice: Irrigation decision-making needs to consider future rainfall |journal=Agricultural Water Management |volume=280 |article-number=108196 |doi=10.1016/j.agwat.2023.108196 |bibcode=2023AgWM..28008196Z |issn=0378-3774|doi-access=free }}</ref> Plants that thrive in drier climates thrive in conditions with infrequent, large rainfall events, while plants in wetter ecosystems prefer the opposite: frequent, mild rainfall.<ref>{{Cite journal |last1=Feldman |first1=Andrew F. |last2=Feng |first2=Xue |last3=Felton |first3=Andrew J. |last4=Konings |first4=Alexandra G. |last5=Knapp |first5=Alan K. |last6=Biederman |first6=Joel A. |last7=Poulter |first7=Benjamin |date=2024 |title=Plant responses to changing rainfall frequency and intensity |url=https://www.nature.com/articles/s43017-024-00534-0 |journal=Nature Reviews Earth & Environment |language=en |volume=5 |issue=4 |pages=276–294 |doi=10.1038/s43017-024-00534-0 |bibcode=2024NRvEE...5..276F |issn=2662-138X|url-access=subscription }}</ref>
In areas with wet and dry seasons, [[soil]] nutrients diminish and erosion increases during the wet season.<ref name="JS"/> Animals have adaptation and survival strategies for the wetter regime. The previous dry season leads to food shortages into the wet season, as the crops have yet to mature.<ref>{{cite book|author=A. Roberto Frisancho|author-link=A. Roberto Frisancho|title=Human Adaptation and Accommodation|url=https://archive.org/details/humanadaptationa0000fris|url-access=registration|year=1993|publisher=University of Michigan Press|isbn=978-0-472-09511-7|page=[https://archive.org/details/humanadaptationa0000fris/page/388 388]}}</ref> Developing countries have noted that their populations show seasonal weight fluctuations due to food shortages seen before the first harvest, which occurs late in the wet season.<ref>{{cite journal |author=Marti J. Van Liere |author2=Eric-Alain D. Ategbo |author3=Jan Hoorweg |author4=Adel P. Den Hartog |author5=Joseph G. A. J. Hautvast|title=The significance of socio-economic characteristics for adult seasonal body-weight fluctuations: a study in north-western Benin|journal=British Journal of Nutrition|year=1994|volume=72|pages=479–488|doi=10.1079/BJN19940049|pmid=7947661|issue=3|doi-access=free}}</ref> Rain may be [[Rainwater harvesting|harvested]] through the use of [[rainwater tank]]s; treated to potable use or for non-potable use indoors or for irrigation.<ref>{{cite web|url=http://rainwaterharvesting.tamu.edu/drinking/gi-366_2021994.pdf |title=Harvesting, Storing, and Treating Rainwater for Domestic Indoor Use |author=Texas Department of Environmental Quality |publisher=Texas A&M University |date=16 January 2008 |access-date=15 January 2010 |archive-url=https://web.archive.org/web/20100626112252/http://rainwaterharvesting.tamu.edu/drinking/gi-366_2021994.pdf |archive-date=26 June 2010 }}</ref> Excessive rain during short periods of time can cause [[flash flood]]s.<ref>{{cite web|url=http://amsglossary.allenpress.com/glossary/search?p=1&query=flash+flood&submit=Search|title=Flash Flood|author=Glossary of Meteorology|publisher=[[American Meteorological Society]]|date=June 2000|access-date=15 January 2010|archive-url=https://web.archive.org/web/20120111195417/http://amsglossary.allenpress.com/glossary/search?p=1&query=flash+flood&submit=Search|archive-date=11 January 2012}}</ref>
===Culture and religion===
{{See also|List of rain deities}}
[[File:Harar Dance.jpg|thumb|alt=photograph|A [[Rainmaking (ritual)|rain dance]] being performed in [[Harar]], [[Ethiopia]]]]
Cultural attitudes towards rain differ across the world. In [[temperate climate]]s, people tend to be more stressed when the weather is unstable or cloudy, with its impact greater on men than women.<ref>{{cite journal|title=The effect of weather on mood, productivity, and frequency of emotional crisis in a temperate continental climate|journal=International Journal of Biometeorology|doi=10.1007/BF01044907|volume=32|date=10 December 1986|author=A. G. Barnston|pages=134–143|issue=4|pmid=3410582|bibcode=1988IJBm...32..134B |s2cid=31850334|url=https://zenodo.org/record/1232480}}</ref> Rain can also bring joy, as some consider it to be soothing or enjoy the aesthetic appeal of it. In dry places, such as India,<ref>{{cite web|url=http://www.thaindian.com/newsportal/enviornment/sudden-spell-of-rain-lifts-mood-in-delhi_100172192.html|title=Sudden spell of rain lifts mood in Delhi|date=23 March 2009|access-date=15 January 2010|author=IANS|work=Thaindian News |url-status=live|archive-url=https://web.archive.org/web/20121016051410/http://www.thaindian.com/newsportal/enviornment/sudden-spell-of-rain-lifts-mood-in-delhi_100172192.html|archive-date=16 October 2012}}</ref> or during periods of [[drought]],<ref>{{cite web|url=http://www.mysanantonio.com/business/Rain_lifts_mood_of_farmers.html|title=Rain lifts moods of farmers|date=11 September 2009|access-date=15 January 2010|first=William|last=Pack|publisher=[[San Antonio Express-News]]|url-status=live|archive-url=https://web.archive.org/web/20121003054311/http://www.mysanantonio.com/business/local/article/Rain-lifts-mood-of-farmers-843592.php|archive-date=3 October 2012}}</ref> rain lifts people's moods. In [[Botswana]], the [[Setswana]] word for rain, ''pula'', is used as [[Botswana pula|the name of the national currency]], in recognition of the economic importance of rain in its country, since it has a desert climate.<ref>{{cite web|url=http://www.pulapulapula.co.uk/Glossary.html|title=Glossary of Setswana and Other Words|author=Robyn Cox|year=2007|access-date=15 January 2010|url-status=usurped|archive-url=https://web.archive.org/web/20120801074955/http://www.pulapulapula.co.uk/Glossary.html|archive-date=1 August 2012}}</ref> Several cultures have developed means of dealing with rain and have developed numerous protection devices such as [[umbrella]]s and [[raincoat]]s, and diversion devices such as [[rain gutter|gutters]] and [[storm drain]]s that lead rains to sewers.<ref>{{cite book|url=http://unix.eng.ua.edu/~rpitt/Publications/BooksandReports/Stormwater%20Effects%20Handbook%20by%20%20Burton%20and%20Pitt%20book/chp1.pdf|page=4|year=2002|author1=Allen Burton|author2=Robert Pitt|name-list-style=amp|title=Stormwater Effects Handbook: A Toolbox for Watershed Managers, Scientists, and Engineers|publisher=CRC Press, LLC|access-date=15 January 2010|url-status=live|archive-url=https://web.archive.org/web/20100611003049/http://unix.eng.ua.edu/~rpitt/Publications/BooksandReports/Stormwater%20Effects%20Handbook%20by%20%20Burton%20and%20Pitt%20book/chp1.pdf|archive-date=11 June 2010}}</ref> Many people find the scent during and immediately after rain pleasant or distinctive. The source of this scent is [[petrichor]], an oil produced by plants, then absorbed by rocks and soil, and later released into the air during rainfall.<ref name="Bear1964">{{Cite journal|volume=201|issue=4923|pages=993–995|last1=Bear|first1=I.J.|first2=R.G.|last2=Thomas|title=Nature of argillaceous odour|journal=Nature|date=March 1964|doi=10.1038/201993a0|bibcode=1964Natur.201..993B|s2cid=4189441}}</ref>
[[File:Nuremberg Chronicle f 029r 2.png|thumb|upright=0.6|Rain, depicted in the 1493 ''[[Nuremberg Chronicle]]'']]
Rain holds an important religious significance in many cultures.<ref name="Mersereau">{{cite news|last1=Merseraeu|first1=Dennis|title=Praying for rain: the intersection of weather and religion|url=https://www.washingtonpost.com/news/capital-weather-gang/wp/2013/08/26/praying-for-rain-the-intersection-of-weather-and-religion/|newspaper=The Washington Post|agency=WP Company LLC|publisher=Nash Holdings LLC|date=26 August 2013}}</ref> The ancient [[Sumer]]ians believed that rain was the [[semen]] of the [[Sky deity|sky god]] [[Anu|An]],<ref name="NemetNajat1996">{{citation|last=Nemet-Nejat|first=Karen Rhea|date=1998|title=Daily Life in Ancient Mesopotamia|publisher=Greenwood|isbn=978-0313294976|pages=[https://archive.org/details/dailylifeinancie00neme/page/181 181–182]|url=https://archive.org/details/dailylifeinancie00neme/page/181}}</ref> which fell from the heavens to inseminate his consort, the [[earth goddess]] [[Ki (goddess)|Ki]],<ref name="NemetNajat1996"/> causing her to give birth to all the plants of the earth.<ref name="NemetNajat1996"/> The [[Akkadian Empire|Akkadians]] believed that the clouds were the breasts of Anu's consort [[Antu (goddess)|Antu]]<ref name="NemetNajat1996"/> and that rain was milk from her breasts.<ref name="NemetNajat1996"/> According to Jewish tradition, in the first century BC, the Jewish miracle-worker [[Honi ha-M'agel]] ended a three-year drought in [[Judea (Roman province)|Judaea]] by drawing a circle in the sand and praying for rain, refusing to leave the circle until his prayer was granted.<ref>{{cite book|last1=Simon-Shoshan|first1=Moshe|title=Stories of the Law: Narrative Discourse and the Construction of Authority in the Mishnah|date=2012|publisher=Oxford University Press|___location=Oxford, England|isbn=978-0-19-977373-2|pages=156–159|url=https://books.google.com/books?id=p5tpAgAAQBAJ}}</ref> In his ''[[Meditations]]'', the Roman emperor [[Marcus Aurelius]] preserves a prayer for rain made by the [[Athens|Athenians]] to the Greek sky god [[Zeus]].<ref name="Mersereau"/> Various [[Indigenous peoples of the Americas|Native American]] tribes are known to have historically conducted [[Rainmaking (ritual)|rain dances]] in effort to encourage rainfall.<ref name="Mersereau"/> Rainmaking rituals are also important in many African cultures.<ref>{{cite book|last1=Chidester|first1=David|last2=Kwenda|first2=Chirevo|last3=Petty|first3=Robert|last4=Tobler|first4=Judy|last5=Wratten|first5=Darrel|title=African Traditional Religion in South Africa: An Annotated Bibliography|date=1997|publisher=ABC-CLIO|___location=Westport, Connecticut|isbn=978-0-313-30474-3|page=280|url=https://books.google.com/books?id=8rGpO_TzeCsC&pg=PA280}}</ref> In the present-day United States, various [[Governor (United States)|state governors]] have held [[Day of Prayer|Days of Prayer]] for rain, including the [[Days of Prayer for Rain in the State of Texas]] in 2011.<ref name="Mersereau"/>
==Global climatology==
{{See also|Earth rainfall climatology}}
Approximately {{convert|505000|km3|mi3|abbr=on}} of water falls as precipitation each year across the globe with {{convert|398000|km3|mi3|abbr=on}} of it over the oceans.<ref name="chow">{{cite web|author=Chowdhury's Guide to Planet Earth|year=2005|url=http://www.planetguide.net/book/chapter_2/water_cycle.html|title=The Water Cycle|publisher=WestEd|access-date=24 October 2006|archive-url=https://web.archive.org/web/20111226143942/http://www.planetguide.net/book/chapter_2/water_cycle.html|archive-date=26 December 2011}}</ref> Given the Earth's surface area, that means the globally averaged annual precipitation is {{convert|990|mm|in|abbr=on}}. Deserts are defined as areas with an average annual precipitation of less than {{convert|250|mm|0|abbr=on}} per year,<ref name="usgsdesert">{{cite web|url=http://pubs.usgs.gov/gip/deserts/what/|title=What is a desert?|author=Publications Service Center|publisher=[[United States Geological Survey]]|access-date=15 January 2010|date=18 December 2001|url-status=live|archive-url=https://web.archive.org/web/20100105030144/http://pubs.usgs.gov/gip/deserts/what/|archive-date=5 January 2010}}</ref><ref>According to [http://pubs.usgs.gov/gip/deserts/what/ What is a desert?] {{webarchive|url=https://web.archive.org/web/20101105183042/http://pubs.usgs.gov/gip/deserts/what/ |date=5 November 2010 }}, the 250 mm threshold definition is attributed to [[Peveril Meigs]].</ref> or as areas where more water is lost by [[evapotranspiration]] than falls as precipitation.<ref name="brittanica">{{cite web | url = http://www.britannica.com/eb/article-70815/desert | title = desert | access-date = 9 February 2008 | website = Encyclopædia Britannica online | url-status=live | archive-url = https://web.archive.org/web/20080202110904/http://www.britannica.com/eb/article-70815/desert | archive-date = 2 February 2008 }}</ref>
===Deserts===
{{Main|Desert}}
[[File:deserts.png|thumb|upright=1.35|Largest deserts]]
[[File:Towering Verticle Thunderhead.jpg|thumb|left|Isolated towering vertical desert shower]]
The northern half of Africa is dominated by the world's most extensive hot, dry region, the [[Sahara Desert]]. Some deserts also occupy much of southern Africa: the [[Namib]] and the [[Kalahari]]. Across Asia, a large annual rainfall minimum, composed primarily of deserts, stretches from the [[Gobi Desert]] in Mongolia west-southwest through western Pakistan ([[Balochistan]]) and Iran into the [[Arabian Desert]] in Saudi Arabia. Most of Australia is semi-arid or desert,<ref>{{cite web
| url = http://www.deh.gov.au/biodiversity/about-biodiversity.html
| title = About Biodiversity
| access-date = 18 September 2007
| publisher = Department of the Environment and Heritage
| archive-url = https://web.archive.org/web/20070205015628/http://www.environment.gov.au/biodiversity/about-biodiversity.html
| archive-date = 5 February 2007
}}</ref> making it the world's driest inhabited continent. In South America, the [[Andes]] mountain range blocks Pacific moisture that arrives in that continent, resulting in a desert-like climate just downwind across western Argentina.<ref name="Andes"/> The drier areas of the United States are regions where the [[Sonoran Desert]] overspreads the Desert Southwest, the Great Basin, and central Wyoming.<ref name="USatl">{{cite web|date=17 September 2009 |author=NationalAtlas.gov |publisher=[[United States Department of the Interior]] |url=http://www.nationalatlas.gov/printable/precipitation.html |title=Precipitation of the Individual States and of the Conterminous States |access-date=15 January 2010 |archive-url=https://web.archive.org/web/20100315074458/http://www.nationalatlas.gov/printable/precipitation.html |archive-date=15 March 2010 }}</ref>
===Polar deserts===
{{main|Polar desert|Polar climate}}
Since rain only falls as liquid, it rarely falls when surface temperatures are below freezing unless there is a layer of warm air aloft, in which case it becomes [[freezing rain]]. Due to the entire atmosphere being below freezing, frigid climates usually see very little rainfall and are often known as [[polar desert]]s. A common biome in this area is the [[tundra]], which has a short summer thaw and a long frozen winter. Rainfall in these polar deserts and precipitation in general is very low, though they cannot be described as [[Aridity|arid]], as the soil is predictably moist during brief growing seasons and air humidity remains relatively high, with evaporation rates being very low.<ref>{{Cite book |last=Callaghan |first=Terry V. |chapter-url=https://books.google.com/books?id=QjM0Hb3423EC&pg=PA243 |title=Arctic Climate Impact Assessment - Scientific Report |date=2005-11-07 |publisher=Cambridge University Press |isbn=978-0-521-86509-8 |pages=244–246 |language=en |chapter=Arctic Tundra and Polar Desert Ecosystems}}</ref> Due to its ___location, [[Antarctica]] is home to the driest regions in the world.<ref>{{cite book |url=https://archive.org/details/antarctica-and-the-arctic-circle-2-volumes-a-geographic-encyclopedia-of-the-earths-polar-regions/page/n3/mode/2up?q= |title=Antarctica And The Arctic Circle: A Geographic Encyclopedia of the Earth's Polar Regions |date=2014 |publisher=ABC-CLIO, LLC |isbn=978-1-61069-392-9 |editor1-last=Hund |editor1-first=Andrew J. |volume=1 |pages=362–363}}</ref>
===Rainforests===
{{see also|Rainforest}}
Rainforests are characterized mainly as areas of the world with very high humidity. [[Tropical rainforest|Tropical]] and [[Temperate rainforest|temperate]] rainforests exist, as do the less common dry rainforests.<ref name=":0">{{cite web |date=2004 |title=Identification of Rainforest: Field Guide |url=https://www.environment.nsw.gov.au/resources/pnf/OGRFreviewFieldGuide.pdf |access-date=6 May 2022 |website=Department of Environment and Conservation |publisher=NSW Government}}</ref> Tropical rainforests occupy a large band of the planet, mainly along the [[equator]], as climates associated with tropical rainforests are most often found within ten degrees of latitude of the equator. They do not experience natural seasons as do many other regions, with the average daylight hours and temperatures remaining fairly constant throughout the year.<ref name="McKnight">{{Cite book |last1=McKnight |first1=Tom L |url=https://archive.org/details/physicalgeographmckn |title=Physical Geography: A Landscape Appreciation |last2=Hess |first2=Darrel |publisher=Prentice Hall |year=2000 |isbn=978-0-13-020263-5 |___location=Upper Saddle River, NJ |chapter=Climate Zones and Types |chapter-url=https://www.seaclean.no |url-access=registration |chapter-url-access=registration}}</ref> Temperate rainforests are often located much further from the equator, but still have high rainfall and in many cases have a closed tree [[Canopy (botany)|canopy]].<ref name="Definition">{{cite web |title=A Review of Past and Current Research |url=http://www.inforain.org/rainforestatlas/rainforestatlas_page2.html |url-status=dead |archive-url=https://web.archive.org/web/20121216092224/http://www.inforain.org/rainforestatlas/rainforestatlas_page2.html |archive-date=2012-12-16 |access-date=2008-10-23 |publisher=Ecotrust}}</ref> Dry rainforests maintain a dense canopy, but can face periods of [[drought]].<ref>{{Cite web |last=Grimshaw |first=Paul |date=2017-07-03 |title=Dry Rainforests of SEQ |url=https://www.lfwseq.org.au/dry-rainforests-seq/ |access-date=2025-07-23 |website=Land for Wildlife |language=en-AU}}</ref><ref name=":0" />
===Monsoons===
{{See also|Monsoon|Monsoon trough}}
The equatorial region near the [[Intertropical Convergence Zone]] (ITCZ), or monsoon trough, is the wettest portion of the world's continents. Annually, the rain belt within the tropics marches northward by August, then moves back southward into the [[Southern Hemisphere]] by February and March.<ref>{{cite web|url=http://jisao.washington.edu/data/ud/africa/|publisher=[[University of Washington]]|title=Africa Rainfall Climatology|author=Todd Mitchell|date=October 2001|access-date=2 January 2010|url-status=live|archive-url=https://web.archive.org/web/20090924024033/http://jisao.washington.edu/data/ud/africa/|archive-date=24 September 2009}}</ref> Within Asia, rainfall is favored across its southern portion from India east and northeast across the Philippines and southern China into Japan due to the monsoon advecting moisture primarily from the [[Indian Ocean]] into the region.<ref>{{cite journal|url=http://airsea-www.jpl.nasa.gov/publication/paper/CARRS-ms5.pdf|title=Monsoon, Orography, and Human Influence on Asian Rainfall|journal=Proceedings of the First International Symposium in Cloud-prone & Rainy Areas Remote Sensing (CARRS), Chinese University of Hong Kong|author1=W. Timothy Liu|author2=Xiaosu Xie|author3=Wenqing Tang|name-list-style=amp|year=2006|access-date=4 January 2010|archive-url=https://web.archive.org/web/20100527145012/http://airsea-www.jpl.nasa.gov/publication/paper/CARRS-ms5.pdf|archive-date=27 May 2010}}</ref> The monsoon trough can reach as far north as the [[40th parallel north|40th parallel]] in East Asia during August before moving southward after that. Its poleward progression is accelerated by the onset of the summer monsoon, which is characterized by the development of lower air pressure (a [[thermal low]]) over the warmest part of Asia.<ref name="NCFMRF">{{cite web|author=National Centre for Medium Range Forecasting |date=23 October 2004 |url=http://www.ncmrwf.gov.in/Chapter-II.pdf |title=Chapter-II Monsoon-2004: Onset, Advancement and Circulation Features |publisher=India Ministry of Earth Sciences |access-date=3 May 2008 |archive-url=https://web.archive.org/web/20110721161408/http://www.ncmrwf.gov.in/Chapter-II.pdf |archive-date=21 July 2011 }}</ref><ref>{{cite web|author=Australian Broadcasting Corporation|date=11 August 1999|url=http://www.abc.net.au/storm/monsoon/print.htm|title=Monsoon|website=[[Australian Broadcasting Corporation]] |access-date=3 May 2008|archive-url=https://web.archive.org/web/20010223103812/http://www.abc.net.au/storm/monsoon/print.htm|archive-date=23 February 2001|author-link=Australian Broadcasting Corporation}}</ref> Similar, but weaker, monsoon circulations are present over North America and Australia.<ref>{{cite journal|author1=David J. Gochis |author2=Luis Brito-Castillo |author3=W. James Shuttleworth |name-list-style=amp |title=Hydroclimatology of the North American Monsoon region in northwest Mexico|doi=10.1016/j.jhydrol.2005.04.021|date=2006|pages=53–70|volume=316|journal=[[Journal of Hydrology]]|issue=1–4|bibcode = 2006JHyd..316...53G }}</ref><ref>[[Bureau of Meteorology]]. [http://www.bom.gov.au/weather/sa/giles/climate.shtml Climate of Giles.] {{webarchive|url=https://web.archive.org/web/20080811064933/http://www.bom.gov.au/weather/sa/giles/climate.shtml |date=11 August 2008 }} Retrieved on 3 May 2008.</ref>
During the summer, the Southwest monsoon combined with [[Gulf of California]] and [[Gulf of Mexico]] moisture moving around the [[subtropical ridge]] in the Atlantic Ocean brings the promise of afternoon and evening thunderstorms to the southern tier of the United States as well as the [[Great Plains]].<ref name="JHorel"/> The eastern half of the contiguous United States east of the [[98th meridian west|98th meridian]], the mountains of the [[Pacific Northwest]], and the [[Sierra Nevada (U.S.)|Sierra Nevada]] range are the wetter portions of the nation, with average rainfall exceeding {{convert|30|in|mm|abbr=on|order=flip}} per year.<ref name=autogenerated1>NationalAtlas.gov [http://www.nationalatlas.gov/printable/precipitation.html Precipitation of the Individual States and of the Conterminous States.] {{webarchive|url=https://web.archive.org/web/20100315074458/http://www.nationalatlas.gov/printable/precipitation.html |date=15 March 2010 }} Retrieved on 9 March 2008.</ref> [[Tropical cyclone]]s enhance precipitation across southern sections of the United States,<ref>{{cite journal|url=http://cat.inist.fr/?aModele=afficheN&cpsidt=21888982|title=The Contribution of Eastern North Pacific Tropical Cyclones to the Rainfall Climatology of the Southwest United States|author1=Kristen L. Corbosiero|author2=Michael J. Dickinson|author3=Lance F. Bosart|name-list-style=amp|journal=[[Monthly Weather Review]]|issn=0027-0644|volume=137|pages=2415–2435|issue=8|doi=10.1175/2009MWR2768.1|year=2009|bibcode=2009MWRv..137.2415C|url-status=live|archive-url=https://web.archive.org/web/20120106225345/http://cat.inist.fr/?aModele=afficheN&cpsidt=21888982|archive-date=6 January 2012|doi-access=free}}</ref> as well as [[Puerto Rico]], the [[United States Virgin Islands]],<ref>[[Central Intelligence Agency]]. [https://www.cia.gov/the-world-factbook/countries/virgin-islands/ The World Factbook – Virgin Islands.] Retrieved on 19 March 2008.</ref> the [[Northern Mariana Islands]],<ref>[[BBC]]. [http://www.bbc.co.uk/weather/world/country_guides/results.shtml?tt=TT004880 Weather Centre – World Weather – Country Guides – Northern Mariana Islands.] {{webarchive|url=https://web.archive.org/web/20101119051314/http://www.bbc.co.uk/weather/world/country_guides/results.shtml?tt=TT004880 |date=19 November 2010 }} Retrieved on 19 March 2008.</ref> [[Guam]],<ref name="GuamTyphoons">{{cite report |url=https://www.weather.gov/media/gum/Tropical%20Cyclones%20Affecting%20Guam%20(1671-1990).pdf |title=Tropical Cyclones Affecting Guam (1671-1990) |date=September 1, 1983 |publisher=[[Joint Typhoon Warning Center]] |access-date=September 15, 2023 |archive-url=https://web.archive.org/web/20230510174134/https://www.weather.gov/media/gum/Tropical%20Cyclones%20Affecting%20Guam%20%281671-1990%29.pdf |archive-date=May 10, 2023 |url-status=live}}</ref> and [[American Samoa]].<ref>{{Cite web |title=American Sāmoa |url=https://manoa.hawaii.edu/climate-forum/american-samoa/ |access-date=2025-07-22 |website=Pacific Climate Knowledge Exchange |language=en-US}}</ref>
===Impact of the Westerlies===
{{See also|Westerlies}}
[[File:MeanMonthlyP.gif|thumb|upright=1.35|Long-term mean precipitation by month]]
Westerly flow from the mild North Atlantic leads to wetness across western Europe, in particular Ireland and the United Kingdom, where the western coasts can receive between {{convert|1000|mm|in|abbr=on}}, at sea level and {{convert|2500|mm|in|abbr=on}}, on the mountains of rain per year. [[Bergen]], Norway is one of the more famous European rain-cities with its yearly precipitation of {{convert|2250|mm|in|abbr=on}} on average. During the fall, winter, and spring, Pacific storm systems bring most of [[Hawaii]] and the western United States much of their precipitation.<ref name="JHorel">J. Horel. [http://www.met.utah.edu/jhorel/html/wx/climate/normrain.html Normal Monthly Precipitation, Inches.] {{webarchive|url=https://web.archive.org/web/20060919144341/http://www.met.utah.edu/jhorel/html/wx/climate/normrain.html |date=19 September 2006 }} Retrieved on 19 March 2008.</ref> Over the top of the ridge, the jet stream brings a summer precipitation maximum to the [[Great Lakes]]. Large thunderstorm areas known as [[mesoscale convective complex]]es move through the Plains, Midwest, and Great Lakes during the warm season, contributing up to 10% of the annual precipitation to the region.<ref name="Walker">Walker S. Ashley, Thomas L. Mote, P. Grady Dixon, Sharon L. Trotter, Emily J. Powell, Joshua D. Durkee, and Andrew J. Grundstein. [http://ams.allenpress.com/archive/1520-0493/131/12/pdf/i1520-0493-131-12-3003.pdf Distribution of Mesoscale Convective Complex Rainfall in the United States.] Retrieved on 2 March 2008.</ref>
The [[El Niño-Southern Oscillation]] affects the precipitation distribution by altering rainfall patterns across the western United States,<ref>John Monteverdi and Jan Null. [http://tornado.sfsu.edu/geosciences/elnino/elnino.html Western Region Technical Attachment NO. 97-37 November 21, 1997: El Niño and California Precipitation.] {{webarchive|url=https://web.archive.org/web/20091227155828/http://tornado.sfsu.edu/geosciences/elnino/elnino.html |date=27 December 2009 }} Retrieved on 28 February 2008.</ref> Midwest,<ref>{{cite web|author=Southeast Climate Consortium |date=20 December 2007 |url=http://www.agclimate.org/Development/apps/agClimate/controller/perl/agClimate.pl/agClimate.pl?function=climforecast/outlook.html&___location=local&type |title=SECC Winter Climate Outlook |access-date=29 February 2008 |archive-url=https://web.archive.org/web/20080304212445/http://www.agclimate.org/Development/apps/agClimate/controller/perl/agClimate.pl/agClimate.pl?function=climforecast%2Foutlook.html&___location=local&type |archive-date=4 March 2008 }}</ref><ref>{{cite news|work=Reuters|date=16 February 2007|url=https://www.reuters.com/article/domesticNews/idUSN1619766420070216|title=La Niña could mean dry summer in Midwest and Plains|access-date=29 February 2008|url-status=live|archive-url=https://web.archive.org/web/20080421224855/http://www.reuters.com/article/domesticNews/idUSN1619766420070216|archive-date=21 April 2008}}</ref> the Southeast,<ref>[[Climate Prediction Center]]. [http://www.cpc.noaa.gov/products/analysis_monitoring/ensocycle/ensorain.shtml El Niño (ENSO) Related Rainfall Patterns Over the Tropical Pacific.] {{webarchive|url=https://web.archive.org/web/20100528035733/http://www.cpc.noaa.gov/products/analysis_monitoring/ensocycle/ensorain.shtml |date=28 May 2010 }} Retrieved on 28 February 2008.</ref> and throughout the tropics. There is also evidence that [[global warming]] leads to increased precipitation and higher frequency of extreme precipitation events in the eastern portions of North America, while rainfall is becoming less frequent and in lower amounts in the tropics, subtropics, and the western United States.<ref>{{Cite journal |last1=Papalexiou |first1=Simon Michael |last2=Montanari |first2=Alberto |date=2019 |title=Global and Regional Increase of Precipitation Extremes Under Global Warming |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018WR024067 |journal=Water Resources Research |language=en |volume=55 |issue=6 |pages=4901–4914 |doi=10.1029/2018WR024067 |bibcode=2019WRR....55.4901P |issn=0043-1397|url-access=subscription }}</ref>
===Wettest known locations===
[[Cherrapunji]], situated on the southern slopes of the [[Himalaya|Eastern Himalaya]] in [[Shillong]], India, is the confirmed wettest place on Earth, with an average annual rainfall of {{convert|11430|mm|in|abbr=on}}. The highest recorded rainfall in a single year was {{convert|22987|mm|in|abbr=on}} in 1861. The 38-year average at nearby [[Mawsynram]], [[Meghalaya]], India, is {{convert|11873|mm|in|abbr=on}}.<ref>{{cite web|url=http://www.clas.ufl.edu/users/jsouthwo/web/6-per-page-Wettest-Mawsynram-in-India.pdf|archive-url=https://www.webcitation.org/5nAoRHbtP?url=http://www.clas.ufl.edu/users/jsouthwo/web/6-per-page-Wettest-Mawsynram-in-India.pdf|archive-date=30 January 2010|title=Mawsynram in India|first=A. J. |last=Philip|date=12 October 2004|publisher=[[Tribune News Service]]|access-date=5 January 2010}}</ref> The wettest spot in Australia is [[Mount Bellenden Ker]] in the north-east of the country which records an average of {{convert|8000|mm|in|abbr=on}} per year, with over {{convert|12200|mm|in|1|abbr=on}} of rain recorded during 2000.<ref>{{cite web |title = Significant Weather – December 2000 (Rainfall) |url = http://www.bom.gov.au/inside/services_policy/public/sigwxsum/sigw1200.shtml#rain |publisher = Commonwealth of Australia|author=Bureau of Meteorology |year=2010|access-date = 15 January 2010|author-link = Bureau of Meteorology }}</ref> The [[Big Bog, Maui|Big Bog]] on the island of [[Maui]] has the highest average annual rainfall in the Hawaiian Islands, at {{convert|404|in|mm|abbr=on|order=flip}}.<ref>{{cite web
| url = https://www.wunderground.com/blog/weatherhistorian/new-wettest-___location-for-the-usa-discovered.html
| title = New Wettest Location for U.S.A. Discovered?
| last = Burt
| first = Christopher
| date = 15 May 2012
| website = Weather Underground
| access-date = 30 August 2018
| quote = 30-year mean precipitation at Big Bog for the POR of 1978–2007 is 404.4 }}</ref> [[Mount Waialeale|Mount Waiʻaleʻale]] on the island of [[Kauaʻi]] achieves similar {{anchor|Torrential rain}}torrential rains, while slightly lower than that of the Big Bog, at {{convert|373|in|mm|abbr=on|order=flip}}<ref>{{cite web
| url = https://wrcc.dri.edu/cgi-bin/cliMAIN.pl?hi6565
| title = Mt Waialeale 1047, Hawaii (516565)
| date = 1 August 2008
| website = WRCC
| publisher = NOAA
| access-date = 30 August 2018 }}</ref> of rain per year over the last 32 years, with a record {{convert|17340|mm|in|abbr=on}} in 1982. Its summit is considered one of the rainiest spots on earth, with a reported 360 days of rain per year.<ref>{{Cite book |last=Simons |first=Paul |url=http://archive.org/details/weirdweather0000simo_j1n7 |title=Weird weather |date=1996 |publisher=Little, Brown |others=Internet Archive |isbn=978-0-316-79179-3 |___location=Boston |pages=300}}</ref>
[[Lloró]], a town situated in [[Chocó Department|Chocó]], [[Colombia]], is probably the place with the largest rainfall in the world, averaging {{convert|523.6|in|mm|abbr=on|order=flip}} per year.<ref name="NCDCxrain">{{cite web|url=http://www.ncdc.noaa.gov/oa/climate/globalextremes.html|title=Global Measured Extremes of Temperature and Precipitation|author=National Climatic Data Center|date=9 August 2005|access-date=18 January 2007|publisher=[[National Oceanic and Atmospheric Administration]]|url-status=live|archive-url=https://web.archive.org/web/20020927021958/http://www0.ncdc.noaa.gov/oa/climate/globalextremes.html|archive-date=27 September 2002|author-link=National Climatic Data Center}}</ref> The Department of Chocó is extraordinarily humid. Tutunendaó, a small town situated in the same department, is one of the wettest estimated places on Earth, averaging {{convert|11394|mm|in|abbr=on}} per year; in 1974 the town received {{convert|26303|mm|ftin|abbr=on}}, the largest annual rainfall measured in Colombia. Unlike Cherrapunji, which receives most of its rainfall between April and September, Tutunendaó receives rain almost uniformly distributed throughout the year.<ref>{{cite web |title = Tutunendaó, Choco: la ciudad colombiana es muy lluviosa |url = http://www.elperiodico.com/default.asp?idpublicacio_PK=46&idioma=CAS&idnoticia_PK=523370&idseccio_PK=1038 |language = es |work = El Periódico |first = Alfred |last=Rodríguez Picódate |date = 7 February 2008 |access-date = 11 December 2008 |archive-date = 15 May 2016 |archive-url = http://arquivo.pt/wayback/20160515185311/http://www.elperiodico.com/default.asp?idpublicacio_PK=46&idioma=CAS&idnoticia_PK=523370&idseccio_PK=1038 |url-status = dead }}</ref> [[Quibdó]], the capital of Chocó, receives the most rain in the world among cities with over 100,000 inhabitants: {{convert|354|in|mm|abbr=on|order=flip}} per year.<ref name="NCDCxrain"/>
{| class="wikitable" style="margin:auto;"
|-
!rowspan=2| Continent
!colspan=2| Highest average
!rowspan=2| Place
!colspan=2| Elevation
!rowspan=2| Years of record
|-
!in!!mm
!ft!!m
|-
| South America
| {{convert|523.6|in|mm|0|disp=table}}
| [[Lloró]], [[Colombia]] (estimated){{ref label|a|a|a}}{{ref label|b|b|none}}
| {{convert|520|ft|m|0|disp=table}}{{ref label|c|c|none}}
| 29
|-
| Asia
|{{convert|467.4|in|mm|0|disp=table}}
| [[Mawsynram]], India{{ref label|a|a|b}}{{ref label|d|d|none}}
| {{convert|4597|ft|m|0|disp=table}}|| 39
|-
| Africa
|{{convert|405.0|in|mm|0|disp=table}}
| [[Debundscha]], [[Cameroon]]
| {{convert|30|ft|m|1|disp=table}}|| 32
|-
| [[Oceania]]
| {{convert|404.3|in|mm|0|disp=table}}
| [[Big Bog, Maui]], [[Hawaii Islands|Hawaii (US)]]{{ref label|a|a|c}}
| {{convert|5148|ft|m|0|disp=table}}
| 30
|-
| South America
|{{convert|354.0|in|mm|0|disp=table}}
| [[Quibdo]], Colombia
| {{convert|120|ft|m|1|disp=table}}
| 16
|-
| [[Australia (continent)|Australia]]
| {{convert|340.0|in|mm|0|disp=table}}
| [[Mount Bellenden Ker]], [[Queensland]]
| {{convert|5102|ft|m|0|disp=table}}
| 9
|-
| North America
| {{convert|256.0|in|mm|0|disp=table}}
| [[Hucuktlis Lake]], [[British Columbia]]
| {{convert|12|ft|m|2|disp=table}}
| 14
|-
| [[Europe]]
| {{convert|183.0|in|mm|0|disp=table}}
| [[Crkvice, Montenegro|Crkvice]], [[Montenegro]]
| {{convert|3337|ft|m|0|disp=table}}
| 22
|-
| colspan=7 style="text-align:center;"|'''Source''' (without conversions): ''Global Measured Extremes of Temperature and Precipitation'', [[National Climatic Data Center]]. 9 August 2004.<ref>{{cite web|title=Global Measured Extremes of Temperature and Precipitation#Highest Average Annual Precipitation Extremes|url=http://www.ncdc.noaa.gov/oa/climate/globalextremes.html#highpre|publisher=[[National Climatic Data Center]]|date=9 August 2004|url-status=live|archive-url=https://web.archive.org/web/20020927021958/http://www0.ncdc.noaa.gov/oa/climate/globalextremes.html#highpre|archive-date=27 September 2002}}</ref>
|}
{| class="wikitable" style="margin:auto;"
|-
!rowspan=2|
!rowspan=2| Continent
!rowspan=2| Place
!colspan=2| Highest rainfall
|-
!in!!mm
|-
! Highest average annual rainfall<ref name="Global extremes"/>
| Asia
| [[Mawsynram, India]]
| {{convert|467.4|in|mm|-1|disp=table}}
|-
! Highest in one year<ref name="Global extremes">{{cite web |url= http://wmo.asu.edu/#global |title= Global Weather & Climate Extremes |publisher= World Meteorological Organization |access-date= 18 April 2013 |url-status=live |archive-url= https://web.archive.org/web/20131213113854/http://wmo.asu.edu/#global |archive-date= 13 December 2013 }}</ref>
| Asia
| [[Cherrapunji, India]]
| {{convert|1,042|in|mm|-1|disp=table}}
|-
! Highest in one calendar month<ref>{{Cite web |last=US Department of Commerce |first=NOAA |title=HDSC World Record Point Precipitation Measurements |url=https://www.weather.gov/owp/hdsc_world_record |access-date=2025-07-22 |website=www.weather.gov |language=EN-US}}</ref>
| Asia
| Cherrapunji, India
| {{convert|366|in|mm|0|disp=table}}
|-
! Highest in 24 hours<ref name="Global extremes"/>
| [[Indian Ocean]]
| Foc Foc, [[La Réunion]]
| {{convert|71.8|in|mm|-1|disp=table}}
|-
! Highest in 12 hours<ref name="Global extremes"/>
| Indian Ocean
| Foc Foc, La Réunion
| {{convert|45.0|in|mm|-1|disp=table}}
|-
! Highest in one minute<ref name="Global extremes"/>
| North America
| [[Unionville, Talbot County, Maryland|Unionville, Maryland]], US
| {{convert|1.23|in|mm|1|disp=table}}
|}
== See also ==
{{portal|Ecology|Environment|Water|Weather}}
{{div col|colwidth=30em}}
* [[Aquifer storage and recovery]]
* [[
* [[
* [[
* [[
* [[Hydropower]]
* [[Integrated urban water management]]
* [[Intensity-duration-frequency curve]]
* [[
* [[
* [[Petrichor]] – the cause of the scent during and after rain
* [[Precipitation types]]
* [[Rain dust]]
* [[Rain garden]]
* [[Rain sensor]]
* [[Rainbow]]
* [[Raining animals]]
* [[Rainmaking (ritual)|Rainmaking]]
* [[Rainwater harvesting]]
* [[Rainwater management]]
* [[Red rain]]
* [[Red rain in Kerala]]
* [[Sanitary sewer overflow]]
* [[Sediment precipitation]]
* [[Vortex filter]]
* [[Water resources]]
* [[Water-sensitive urban design]]
* [[Weather]]
{{div col end}}
==Notes==
*{{note label|a|a|a}}{{note label|a|a|b}}{{note label|a|a|c}} The value given is the continent's highest, and ''possibly'' the world's, depending on measurement practices, procedures and period of record variations.
*{{note label|b|b|none}} The official greatest average annual precipitation for South America is {{convert|354|in|cm|order=flip|abbr=on}} at Quibdó, Colombia. The {{convert|523.6|in|cm|order=flip|abbr=on}} average at Lloró [{{convert|14|mi|km|order=flip|abbr=on}} SE and at a higher elevation than Quibdó] is an estimated amount.
*{{note label|c|c|none}} Approximate elevation.
*{{note label|d|d|none}} Recognized as "The Wettest place on Earth" by the ''[[Guinness Book of World Records]]''.<ref name="wett">{{Cite web |url=http://www.clas.ufl.edu/users/jsouthwo/web/6-per-page-Wettest-Mawsynram-in-India.pdf |title=UFL – Dispute between Mawsynram and Cherrapunji for the rainiest place in the world |access-date=5 January 2010 |archive-url=https://www.webcitation.org/5nAoRHbtP?url=http://www.clas.ufl.edu/users/jsouthwo/web/6-per-page-Wettest-Mawsynram-in-India.pdf |archive-date=30 January 2010 }}</ref>
*{{note label|e|e|none}} This is the highest figure for which records are available. The summit of [[Mount Snowdon]], about {{convert|500|yards|meters}} from Glaslyn, is estimated to have at least {{convert|200.0|in|mm}} per year.
==References==
{{reflist|2}}
==External links==
{{wikiquote}}
{{commons|Rain}}
*[http://news.bbc.co.uk/2/hi/sci/tech/146120.stm BBC article on the weekend rain effect]
*[http://news.bbc.co.uk/2/hi/asia-pacific/3893671.stm BBC article on rain-making]
*[http://news.bbc.co.uk/1/hi/magazine/4562132.stm BBC article on the mathematics of running in the rain]
*[http://www.geography-site.co.uk/pages/physical/climate/why%20does%20it%20rain.html What are clouds, and why does it rain?]
{{natural resources|state=collapsed}}
{{Nature}}
{{good article}}
{{Authority control}}
[[Category:Articles containing video clips]]
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