*2.1. Study Area*

As shown in Figure 1, the North China Plain (NCP) is located between 32◦–40◦ N and 114◦–121◦ E along the east coast of China. It represents 1 of the 3 major plains in China,

including Beijing, Tianjin, 9 cities in the Hebei Province, 15 cities in the Henan Province, 16 cities in the Shandong Province, 6 cities in the Anhui Province, and 5 cities in the Jiangsu Province. The names and abbreviations of all cities are shown in Table S1. The study area extends from the south foot of Yanshan Mountain in the north, Taihang Mountain and Funiu Mountain in the west, Dabie Mountain in the south, and the Bohai and Yellow Seas in the east. The total area of the study region is 300,000 km2. The topography is flat and low in altitude, with numerous rivers and lakes and a dense population. Most cities in the study area are characterized by a temperate monsoon climate, whereas a few provinces (such as Jiangsu and Anhui) have a subtropical monsoon climate. The four seasons of the study region have been changing significantly, driven by the monsoon climate. The region is characterized by hot and rainy summers, while winters are cold and dry. The precipitation mostly occurs between June and September. Notably, the region stands out with exceptional natural conditions, rendering it an important grain base and geographical space in China [21–23].

**Figure 1.** The geographical location of the study area.
