Analysis of spatial and temporal differences in water conservation function in Zhangjiakou based on the InVEST model

As the water conservation function and ecological environment support area of Beijing, the capital of China, Zhangjiakou plays important roles in protecting ecological security. Based on the InVEST model, this study estimated water yield and water conservation capacity of Zhangjiakou from 1981 to 2015 and analyzed spatial and temporal variation characteristics. The results are as follows. 1) Average annual water yield and water conservation depth of Zhangjiakou was 42.51 and 18.16 mm, respectively. 2) Water yield showed a slight upward trend, while water conservation showed a slightly downward trend in the past 35 years. The highest water yield and water conservation values were recorded in 1995 and the lowest in 1993. 3) Obvious spatial differences were observed in water yield and water conservation depth regardless of similar distribution patterns, indicating that the values around Kangbao and Xuanhua increased but those around Guyuan and Yuxian decreased. 4) Precipitation was the main effect factor for changes in water yield and water conservation in Zhangjiakou, followed by land use. 5) Multi-year average water yield was high in grasslands and farmlands, and water conservation was high in grasslands.