*3.2. Analysis of Spatial Heterogeneity Characteristics of Each Impact Factor* 3.2.1. Identification of Influencing Factors

This paper selected 12 influencing factors from two aspects of society-economy, and natural environment. The values of NDVI, Forest and grass area, Forest and grass coverage ratio, and Proportion of water area were directly or indirectly obtained from the Resource and Environmental Science and Data Center, Chinese Academy of Sciences (http://www. resdc.cn/, accessed on 2 July 2018). All other influence factors were obtained from the statistical yearbook [45–48]. For the three different years of 2010, 2015 and 2020, the collinearity investigation of influencing factors and the significance test between them and the explained variables were carried out respectively, which is the first step in building a model. The specific work was to construct models for different parameter combinations by the OLS model in Arcgis 10.4. Then, parameters, that did not meet the criteria for variance inflation factor (VIF) and significance tests were excluded one by one gradually. The results (Table 5) showed that in the three years, only four influencing factors satisfy the two conditions of being VIF < 7.5 and significant at the same time. Therefore, we selected per capita GDP, population density, the proportion of water areas, and water consumption as the research objects.


**Table 5.** Statistical test results and the selection of influencing factors.
