Comparing GPCP and IMERG in the North American Monsoon Region from 2001-2021

The North American monsoon (NAM) is defined as a change in atmospheric circulation that brings tropical moisture from the Gulf of California, the Gulf of Mexico, and the Pacific and causes precipitation to peak during June-September (JJAS). These regions are often affected by extreme droughts and floods, and rely on the NAM for agriculture and ranches, so understanding the precipitation patterns associated with the NAM is extremely important. This research aims to explore how the NAM is represented in two different precipitation observation datasets. Precipitation data from 2001-2021 in JJAS is from the Global Precipitation Climatology Project (GPCP), available at a 2.5° and 1° horizontal resolution, and NASA’s Global Precipitation Mission (GPM) Integrated Multi-SatellitE Retrievals for GPM (IMERG), available at a 0.1°horizontal resolution. Three regions were analyzed: Arizona and New Mexico (AZNM; 115°-107.5°W, 31-37°N), North-Western Mexico (NWM; 110.5°-103°W, 25°-31°N), and South-Western Mexico (SWM; 105°-97.5°W, 19°-25°N). In general, there is little variation between the three products, however, IMERG generally tends to show higher rates of precipitation, especially in drier regions such as AZNM. IMERG also tends to have a higher percentage of annual precipitation that falls during JJAS. Extreme events were calculated by using the 90th percentile for IMERG Daily 0.1° resolution and GPCP Daily 1° resolution. We found that the number of extreme events could not be explained by the El Niño Southern Oscillation, a dominant mode of climate variability. Future research should focus on how topography and complex terrain affect a precipitation product’s ability to capture NAM precipitation.