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 early detection and monitoring of hydrometeorological hazards. The precipitation product, Integrated Multi-satellitE Retrievals for the Global Precipitation Mission (IMERG), provides NRT 0.1° and 30-minute precipitation estimates across the globe with only a 4-hour latency. This study was an evaluation of the GPM IMERG version 6 level-3 Early Run 30-minute precipitation product for precipitation events from 2014 through 2020. The purpose of this research was to identify when, where, and why GPM IMERG misidentified and failed to detect precipitation events in California, Nevada, Arizona, and Utah in the United States. Precipitation events were identified based on 15-minute precipitation from gauges and 30-minute precipitation from the IMERG multi-satellite constellation. False positive and false negative precipitation events were identified and analyzed to determine characteristics. Precipitation events identified by gauges had longer duration and had higher cumulative precipitation than those identified 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.