Evaluating Precipitation Events Using GPM IMERG 30-Minute Near-Real-Time Precipitation Estimates

Accurately detecting and estimating precipitation at near - real time (NRT) is of utmost importance for the early detection and monitoring of hydrometeorological hazards. The precipitation product, Integrated Multi-satellitE Retrievals for Global Precipitation Measurement (IMERG), provides NRT 0.1 degrees and 30-min precipitation estimates across the globe with only a 4-h latency. This study was an evaluation of the GPM IMERG version 6 level-3 early run 30-min precipitation product for precipitation events from 2014 through 2020. The purpose of this research was to identify when, where, and why GPM IMERG misidenti fi ed and failed to detect precipitation events in California, Nevada, Arizona, and Utah in the United States. Precipitation events were identi fi ed based on 15-min precipitation from gauges and 30-min precipitation from the IMERG multisatellite constellation. False-positive and false-negative precipitation events were identi fi ed and analyzed to determine their characteristics. Precipitation events identi fi ed by gauges had longer duration and had higher cumulative precipitation than those identi fi ed by GPM IMERG. GPM IMERG had many false event detections during the summer months, suggesting possible virga event detection, which is when precipitation falls from a cloud but evaporates before it reaches the ground. The frequency and timing of the merged passive microwave (PMW) product and forward propagation were responsible for IMERG overestimating cumulative precipitation during some precipitation events and underestimating others. This work can inform experts that are using the GPM IMERG NRT product to be mindful of situations where GPM IMERG - estimated precipitation events may not fully resolve the hydrometeorological conditions driving these hazards.