*2.1. Study Area*

The HC is located in Northwest China (92◦12 –104◦20 E, 37◦17 –42◦48 N) (Figure 1a), including the five prefecture-level cities of Wuwei, Jinchang, Zhangye, Jiuquan, and Jiayuguan (Figure 1c, http://srtm.csi.cgiar.org (accessed on 10 August 2021)) [47]. The three major rivers of the HC, from west to east, are the Shule River, the Heihe River and the Shiyang River, originating from the Qilian Mountains. The HC is mainly covered by bare land and gobi, and agricultural land is concentrated in the Shiyang River Basin (SYRB) and Heihe River Basin (HRB) (Figure 1d, https://www.resdc.cn (accessed on 10 August 2021)) [48]. It belongs to the arid continental climate, with an average annual temperature ranging from 8 to 10 ◦C [42], and the annual evaporation is 1500–3200 mm [49]. The rainfall shows a decreasing trend from east to west (Figure 1b, http://data.cma.cn (accessed on 10 August 2021)), and ~80% of rainfall occurs during July–August [50]. The Qilian Mountains in the south nurture extensive glaciers and snow, which is an important freshwater resource for downstream cities critical to easing agricultural drought and other human activities in the HC [51].

**Figure 1.** Information summary of the Hexi corridor: (**a**) geographical location, (**b**) annual precipitation, (**c**) digital elevation and distribution of groundwater-level monitoring points, (**d**) land use.

### *2.2. Materials*
