Annual Total Precipitation

The daily GPM\_3IMERGDF product (365 days) is aggregated into the annual total precipitation for the wet year (2004) and the dry year (2001), and also for the year 2006 and 2012 (i.e., for the verification) @ 0.1◦ spatial resolution as shown in Figure 2h–k, respectively. The equation deriving the annual total precipitation for the mentioned temporal periods is as follows in Equation (3):

$$P\_{\text{GPM}i} = \sum\_{j=1}^{n} P\_{\text{GPM}\_{\text{dndity}-j}} \tag{3}$$

where *PGPMi* is *i*-th annual precipitation (i.e., 2001, 2004, 2006 and 2012,) for the study area, *PGPMdaily*−*<sup>j</sup>* is the daily GPM\_3IMERGDF precipitation for *j*-th day (*n* = 365).

#### 2.2.2. ASTER Global Digital Elevation Model (GDEM)

The ASTER GDEM is released by the Ministry of Economy, Trade and Industry [53] of Japan, and the NASA [38,54]. The ASTER GDEM covers the land surface between 83◦N and 83◦S of the Earth, which includes the entire area of Mainland China. The latest GDEM version 3 was released on August 5, 2019, which added additional stereo-pairs with improved coverage and reducing the occurrence of artifacts. The refined production algorithm provides an improved spatial resolution, increased the horizontal and vertical accuracy [53]. It provides the spatial resolution of one arc-second (approximately 30 m), and is used in this study as an influencing predictor on precipitation (Figure 2a). In addition to the elevation data, two other terrain attributes, i.e., longitude and latitude, are also derived from the ASTER GDEM. The ASTER GDEM data is available at https://search.earthdata.nasa.gov/search/granules (Accessed on 20 June 2020).
