Abstract:Using the daily measured precipitation data of 171 meteorological stations in the Yangtze River Delta from 1961 to 2018, this study evaluated the detection ability of ERA5 reanalysis precipitation data for rainy days, analyzed the accuracy of ERA5 precipitation simulation and the ability of ERA5 to describe extreme precipitation indices. Assessment results showed that ERA5 reanalysis precipitation data could reproduce the precipitation process, with high probability of detection (POD), small equitable threat score (ETS) and low false alarm ratio (FAR). The detection performance in the south of the study area was better than that in the north. The percent of false alarm occurrences for rainy days of ERA5 was about 17.68%, mainly occupied by light rain. ERA5 overestimated the regional multi-year average precipitation by about 15.75%, and the root mean square error (RMSE) was small. The error was also large when the precipitation was large. And the error in the south region was slight higher than that in the north region. ERA5 had a good linear correlation on monthly,seasonal and annual scales. ERA5 showed a trend of overestimation and then underestimation over time for six extreme precipitation indicators such as PRCPTOT, RX5d, R95P, R99P, R20 and R25. And the intensity indices over estimated much higher in the south than those in the north, while the occurrence indices had opposite trend. The three indices RX1d, SDII and CDD had been underestimated, and there was a significantly large underestimation in the north than that in the south. While ERA5 had a continuously overestimation for CWD and R10 with no significant difference between the north and the south.