Earthdata Forum

Answer: Integrated Multi-satellitE Retrievals for Global Precipitation Measurement (IMERG) half-hourly rainfall data is not cumulative. Each half hour's IMERG value is based on a single snapshot that is assumed to apply for the entire half hour (expressed in the intensive units of "mm/hr"). Users can aggregate the time series of values to different time scales (like hourly or daily) to compute cumulative precipitation amounts if needed.

References:

IMERG Volume 7 ALGORITHM THEORETICAL BASIS DOCUMENT (ATBD)

IMERG Technical Documentation