2.2.1. Rain Gauge Data

A gridded precipitation product (0.25◦ × 0.25◦) of the China Gauge-Based Daily Precipitation Analysis (CGDPA) was used as the ground reference dataset. This dataset was produced and is routinely operated by the National Meteorological Information Center (NMIC) of the China Meteorological Administration (CMA). Based on amassing ~2400 gauge stations across Mainland China, the NMIC uses a modified interpolation method of climatology-based optimal interpolation (OI) proposed by Xie et al. [40] to yield the daily gridded CGDPA product. All the gauge data inputted in the CGDPA are manually recorded by bucket rain gauges and must pass a strict quality control procedure including the extreme values' check, internal consistency check, and spatial consistency check [41]. The validation reports of Shen and Xiong [42] demonstrated that the CGDPA is a more reliable precipitation product than other existing surface observation datasets over Mainland China, and the authors recommended it as a reliable ground-based data to various meteorological and hydrological applications. At present, the CGDPA is available as the official gridded daily precipitation dataset in the CMA website and can be downloaded from http://data.cma.cn/site/index.html. Considering the ease of access and high-quality of CGDPA, a large number of studies have used the CGDPA to assess the satellite precipitation products over China [39,43–45]. Figure 1a shows the number of gauge stations in each 0.25◦ grid box of CGDPA. Clearly, about 80% of the gauges are located in the eastern China with low elevations, while relatively sparse gauges are distributed over the western mountains and deserts, especially over the TP.
