How well do satellite and reanalysis precipitation products capture North American monsoon season in Arizona and New Mexico?

Assessment of the precipitation products with ground-based data is essential to building confidence in these datasets. Precipitation products tend to have large errors in semi-arid regions such as the Southwest United States, where accurate precipitation quantification is critical for water resource management and flood mitigation measures. Therefore, this region, with its high density of ground-based data, is important for the evaluation of the products. The Southwest United States is also interesting due to its monsoonal precipitation pattern, in which changes in circulation patterns that bring tropical moisture to the region yield roughly 50% of the region's precipitation between the months of June–September. In the present study, the performance of precipitation products was evaluated over Arizona and New Mexico for the monsoon seasons of the 2002–2021 period, with an emphasis on the recent extreme years of 2020 and 2021. Results indicate that all satellite products tend to capture interannual variations of precipitation rate but struggled to capture high-intensity events. IMERG Final notably has better performance than other products, with the lowest root mean square error and highest correlation with Stage IV, which was 3–60 percent better than other products. IMERG Final had the best detection capacity for rainy days as well. ERA5-Land performed well in capturing the average monsoon precipitation rate; however, showed limited skill in the detection of trace, light, and extreme precipitation events. IMERG Late and PDIR-Now showed difficulty detecting light precipitation events and overestimated extreme events. This study shows the importance of gauge adjustment for satellite products (e.g., IMERG) as well as the need for improvement of reanalysis products over arid regions, and better representation of orographic precipitation.