Performance Assessment of Hourly Precipitation Products from IMERG and GSMaP over Mainland China

Precipitation in China exhibits high diversity and significant regional differences, leading to considerable variability in the applicability of satellite-derived precipitation products. Using hourly surface observations from national meteorological stations (2019–2023), this study evaluates two hourly satellite products—IMERG_V7 (hereafter IMERG) and GSMaP_V8 (hereafter GSMaP)—over mainland China. Spatial patterns and error characteristics are compared across regions, months, and time periods using quantitative and categorical statistics, and applicability under different weather conditions is assessed.The result shows: both products overestimate light precipitation frequency and underestimate heavy precipitation, with GSMaP showing a stronger overestimation of light events and weaker mean intensities. IMERG more closely matches observed intensity distributions and is locally stronger in eastern Northwest and Southwest China. Both perform poorly for persistent autumn–winter rainfall in Southwest China and winter snowfall north of Huang–Huai, though GSMaP shows slightly higher critical success index (CSI) and correlation in these cases. Performance is better for spring rainfall in Jiangnan/Jianghuai and autumn rainfall in the Huai River Basin, but weaker for pre-flood season convection in South China. Overall, IMERG outperforms GSMaP in major rainy seasons, particularly July–August, due to a lower false alarm rate and higher CSI and correlation..