Fig. 1

Study Area: Regions Surrounding the Taihang Mountains. The study area encompasses Beijing (16 districts, covering 16,000 square kilometers with a population of 22Â million), Hebei province (11 cities, 167 districts, covering 188,800 square kilometers with a population of 74Â million), Shanxi province (11 cities, 117 districts, covering 156,700 square kilometers with a population of 35Â million), and Henan province (17 cities, 136 districts, covering 167,000 square kilometers with a population of 98Â million)