*2.1. Study Area*

The study area is the region of mainland China with the longitude and latitude range between 73–135◦E and 18–53◦N, respectively (Figure 1). The spatial distribution of the Digital Elevation Model (DEM) in mainland China is also shown in Figure 1, which demonstrates that the terrain of mainland China is low in the southeast and high in the northwest, forming a three-ladder pattern. Due to the dramatic changes in terrain, the climate in mainland China is of grea<sup>t</sup> complexity and is mainly regulated by the monsoon system [28]. The precipitation in China shows conspicuous variability at both temporal and spatial scales.

**Figure 1.** Spatial distributions of DEM and ground-based rain gauges used in this study across mainland China.

In this study, we chose the northern hemisphere summer (from June to August) of 2018 as the research period. The China Climate Bulletin in 2018 published by the China Meteorological Administration (CMA) shows that the annual average precipitation in China was 673.8 mm/year, which was 7% more than in other years. In particular, the average precipitation in summer was 356.4 mm/year, which was 10% above that of previous summers. Intensive typhoons and heavy rain occurred frequently in the summer of 2018. The East Asian subtropical summer monsoon was significantly stronger than usual in 2018, being the strongest since 1951.

#### *2.2. Gauge Precipitation Measurements*

The hourly rain gauge datasets from 2163 national ground stations used in this study were collected from the National Meteorological Information Center (NMIC) of CMA (http://data.cma.cn). The spatial distribution of ground stations in mainland China is shown in Figure 1. Hourly datasets from national ground stations usually include observations of air temperature, air pressure, precipitation, relative humidity, water vapor pressure, wind, and precipitation, etc. Meanwhile, the ground station datasets are quality controlled with the actual rate of each factor over 99.9%, and the accuracy of the datasets was close to 100% [29].

#### *2.3. Satellite Precipitation Estimates*

#### 2.3.1. FY-2E Quantitative Precipitation Estimates (QPE)

The FY-2 series satellites are the principle observational platforms for covering dynamic weather events and the near-earth space environments in China. FY-2E is the third operational stationary satellite in the FY series, and was launched on 23 December 2008. Its sub-satellite point was 105◦E before 1 July 2015 and has been 86.5◦E over the equator to date. FY-2E is the last satellite in the first generation of Chinese operational meteorological satellites. The satellite is equipped with a five-channel (one visible channel and four infrared channels) scanning radiometer named the Visible and Infrared Spin Scan Radiometer (VISSR). The FY-2E satellite performs much better in terms of the accuracy of the inversion results of geophysical parameters, for example, precipitation, due to technical improvements, such as a reduction of the overlap of infrared spectral channels, compared with previous satellites of the FY-2 series.

FY-2E QPE data, generated by the fusion of FY-2E satellite estimate results and precipitation measurements from rain gauges, was used in this study. The QPE products have four categories at di fferent temporal scales—hourly, three-hourly, six-hourly, and daily—with a spatial resolution of 0.1◦ × 0.1◦. The latency of QPE products yielded by FY-2 series satellites is approximately one hour.
