## 2 Materials and Methods
### Methods  
#### 2.3.1 SWAT Model  
The SWAT model is a long-time basin-distributed hydrological model [18]. It has been extensively used for the simulation and prediction of hydrological processes at the basin scale, with excellent simulation results [28]. In this study, the improved SWAT model by [PERSON] [29] and [PERSON] [30], including an improved snowmelt module and subbasin partitioning, was used to enhance the model simulation accuracy by adding cumulative temperature determination conditions to separate rainfall and snowfall types, while also adding land-use/cover-change nodes to the basin partitioning. The SWAT model automatically divides the URB into 35 subbasins and 76 hydrological response units. The model warm-up period \begin{table}
\begin{tabular}{c c c c c} \hline
**Usage** & **Data Name** & **Data Type** & **Resolution** & **Source** \\ \hline \multirow{8}{*}{For building SWAT model} & ASTER DEM & Raster & 30 m & NASA ([[http://www.nasa.gov](http://www.nasa.gov)]([http://www.nasa.gov](http://www.nasa.gov))) (accessed on 15 February 2020) \\  & Soil types & Raster & 1 km & HWSD ([[http://westds.ucstigs.ac.cn/data/](http://westds.ucstigs.ac.cn/data/)]([http://westds.ucstigs.ac.cn/data/](http://westds.ucstigs.ac.cn/data/)) (accessed on 15 February 2020)) \\  & & & & Environmental Resources and Data Center of Chinese Academy of Sciences ([[http://www.resdc.cn](http://www.resdc.cn)]([http://www.resdc.cn](http://www.resdc.cn)) (accessed on 15 February 2020)) \\  & Land-use/cover & Raster & 1 km & ([[http://www.resdc.cn](http://www.resdc.cn)]([http://www.resdc.cn](http://www.resdc.cn)) (accessed on 15 February 2020)) \\  & & & & China Weather Data Network ([[http://data.cma.cn](http://data.cma.cn)]([http://data.cma.cn](http://data.cma.cn)) (accessed on 15 May 2021)) \\  & Meteorology & Station & Daily scale & Hydrological Yearbook of Inner Mongolia \\  & Measured runoff & Station & Daily scale & Autonomous Region \\  & Snow cover & Raster & 500 m/8 days & MODIS MOD10A1 \\  & ET & Raster & 500 m/8 days & MODIS MOD16A2 \\  & GPP & Raster & 500 m/8 days & MODIS MOD17A2 \\  & NDVI & Raster & 1 km/30 days & MODIS MOD13A3 \\ For evaluating ecosystem quality & LAI & Raster & 500 m/8 days & MODIS MOD15A2 \\  & & & & MODIS MCD12Q1 \\  & LCT & Raster & 500 m/year & ([[https://lpdaacyc.cr.usgs.gov/appeears/](https://lpdaacyc.cr.usgs.gov/appeears/)]([https://lpdaacyc.cr.usgs.gov/appeears/](https://lpdaacyc.cr.usgs.gov/appeears/)) (accessed on 15 May 2021)) \\  & & & & Demographic Data Network \\  & Population & Raster & 1 km & ([[https://www.worldpop.org/](https://www.worldpop.org/)]([https://www.worldpop.org/](https://www.worldpop.org/)) (accessed on 25 May 2021)) \\  & Density & Raster & 1 km & ([[https://www.worldpop.org/](https://www.worldpop.org/)]([https://www.worldpop.org/](https://www.worldpop.org/)) (accessed on 25 May 2021)) \\ \hline \end{tabular}
\end{table} 
Table 1: Introduction to basic data sources. for this study area was 1976-1980, the calibration period was 1981-2000, and the validation period was 2001-2012. The SWAT model can be used to simulate hydrological processes at three times scales, such as daily, monthly, and annual, and the monthly scale is used in this study. The SWAT model determines the basin boundary and divides subbasins by analyzing the slope, slope direction, and elevation of the DEM (Digital Elevation Model) of the study area. On this basis, the hydrological processes under different land-use types and different soil types under climate change are simulated based on the input hydrometeorological data, land-use types, and soil data [10]. To improve the model accuracy, the SUFI-2 algorithm of SWAT-CUP software was used in this study for analyzing model parameter sensitivity and uncertainty [10]. The Nash-Sutcliffe efficiency (\(NSE\)), percentage bias (\(PBIAS\)), and coefficient of determination (\(R^{2}\)) were used to evaluate the model simulation accuracy.