Evaluation of the GPM IMERG product at the hourly timescale over China

More-accurate satellite-based precipitation data are required for the study of hydrological and meteorological phenomena in the face of the rapidly changing climate. In this study, we evaluated IMERG V06 Final Precipitation product (IMERG-F) of the Global Precipitation Measurement (GPM) mission based on China Merged Precipitation Analysis (CMPA) data at the hourly timescale for the period from 2008 to 2017. Results indicated the following: (1) The spatial distribution of precipitation is highly consistent between the CMPA and IMERG product. However, precipitation and precipitation frequency ratios in the IMERG data are both overestimated, by 0.1-0.3 mm/h and 5%-15%, respectively. IMERG product has better ability to estimate precipitation in the east and south of China than in the west of China. The precipitation error is larger during nighttime than daytime, while the frequency ratio error is smaller during nighttime than daytime. (2) The time of maximum precipitation is more consistent between the two products than the time of maximum frequency ratio. The time of maximum precipitation is later in the IMERG product than in the CMPA product in most regions except northwestern China, and the time of maximum frequency ratio is later in most regions. (3) Gauge density has a stronger influence on the mean error in precipitation than the mean error in frequency ratio. The findings of this study could help improve the accuracy of satellite precipitation at the hourly scale and help it become a more important tool in the field of hydrometeorology.