Hydrological Evaluation of CRA40 and ERA5 Reanalysis Precipitation Products over Ganjiang River Basin in Humid Southeastern China

The evaluation of two reanalysis precipitation datasets, CRA40 and ERA5, was conducted over the Ganjiang River Basin, utilizing precipitation records from 37 ground rainfall gauges and surface-observed stream flow data spanning from January 1998 to December 2008. Both CRA40 and ERA5 were found to effectively capture the spatial and temporal precipitation characteristics at the basin scale. However, significant differences in precipitation quality were observed between the two. ERA5 demonstrated superior accuracy in depicting short-term precipitation changes, particularly on a daily basis. In contrast, CRA40 exhibited better performance on a monthly scale, offering more stable and long-term precipitation trends. Simulations of stream flow using the VIC hydrological model driven by these two precipitation products revealed that (1) CRA40 outperformed ERA5 in both daily and monthly stream flow simulations, with a higher Nash-Sutcliffe Efficiency (NSE, 0.65 for CRA40 vs. 0.6 for ERA5) and a greater correlation coefficient (CC, 0.96 for CRA40 vs. 0.91 for ERA5). Although ERA5 had a relatively good CC (0.86 and 0.93 respectively), its NSE was notably poor (0.29 and 0.30 respectively); (2) both CRA40 and ERA5 tended to overestimate stream flows in the basin, especially during the flood season (April-September), with ERA5's overestimation being more evident. This study is anticipated to offer a foundation for selecting reliable reanalysis products for precipitation and hydrological simulations in the Ganjiang River Basin.