Evaluation of the GPM IMERG Precipitation Products Using Rain Gauge Network Dataset over the Tibetan Plateau

This study evaluates the performance of the IMERGV06 hourly rainfall over the TP over the TP during the warm seasons (May to September) from 2015 to 2020. Referencing the high-quality rain gauge network (651 stations) over the TP during this period, the assessment includes the spatial and temporal distribution and their statistic metrics of the IMERG hourly product on a seasonal, monthly and daily scale. Furthermore, the six local daily rainfall categories, based on the observation, are divided to evaluate the performance of the IMERG on different rainfall intensities. The main conclusions are as follows. The average overestimation of the warm-season rainfall over the TP is about 30%. In addition, the large variation between IMERG and observation precipitation appears over the regions with the total seasonal rainfall less than 300 mm. The evaluation metrics illustrates that the IMERG performs better in May with weaker daily rainfall and the deviation to the rain gauges is larger in June and July. Combing with the density trace, six daily rainfall intensity levels are sorted: extreme light daily rainfall ranges from 0.1 to 0.5 mm•d^-1, light rainfall covers from 0.5 to 12 mm•d^-1, moderate rainfall is between 12 to 14.9 mm•d^-1, heavy rainfall is from 14.9 to 20.1 mm•d^-1, torrential rainfall covers from 20.1 to 33.2 mm•d^-1 and extreme torrential rainfall is above 33.2 mm•d^-1. The precipitation intensity of each daily rainfall category shows that the IMERG product overestimates the daily rainfall weaker than light rainfall (0.5 to 12 mm•d^-1), but it underestimates the rainfall stronger than moderate rainfall (beyond 12 mm•d^-1). Combing the POD and FAR results, the IMERG product can estimate the light rainfall with the relative high POD of and the low FAR. But for the daily rainfall stronger than moderate rainfall, the IMERG has the low hit ratio and high false alarm.