# Predicting Runoff from the Weigan River under Climate Change
## 2 Data Sources and Methods  
### Overview of the Study Area  
The upper watershed of the Weigan River out of the mountain pass (80\({}^{\circ}\)15\({}^{\prime}\)-83\({}^{\circ}\)02\({}^{\prime}\) E, 41\({}^{\circ}\)31\({}^{\prime}\)-42\({}^{\circ}\)39\({}^{\prime}\) N) is located in the Aksu region at the southern foot of the middle section of the Tianshan Mountains in Xinjiang, China (Figure 1). The topography of the basin is high in the northwest and low in the southeast, with elevations above 3500 m in the high mountainous areas in the north. The basin is fan-shaped, with a basin area of about 16,792.56 km\({}^{2}\). The study area is located in the hinterland of the Eurasian continent, far from the sea and surrounded by mountains, and it has a continental arid climate with a large temperature difference between day and night, high evaporation and low precipitation. The average multi-year temperature is 1.95 \({}^{\circ}\)C, the average multi-year evaporation is 1139.3 mm, the average multi-year precipitation is 382.62 mm, and the distribution of temperature and precipitation is uneven during the year, which is mainly concentrated in June-August. The Weigan River is a first-class tributary of the Tarium River system, and its upper reaches consist of five tributaries that converge in the southeast corner of the Baicheng Basin, namely, Muzati River, Kapuslang River, Tylervichuk River, Karasu River and Heizi River. The recharge sources of the runoff of the Weigan River are mainly three types: glacial meltwater, snowmelt and rainfall, of which glacial meltwater accounts for about 32.40% of the total runoff [21]. The Heizi reservoir hydrological station was originally located 3 km above the dam site of Kizil reservoir, and after the official construction of Kizil reservoir in 1985, the Heizi reservoir hydrological station was relocated down to 1 km below the cross-section of the dam site and renamed the Heizi Reservoir (II) hydrological station.  
Baicheng County in the study area has a special geographic location, surrounded by mountains, with a terrain of high north and low south and an arid and semi-arid natural environment, and its land-use type is mainly dominated by grassland and unused land. The area of arable land, forest land and construction land in Baicheng County increased year by year from 2005 to 2015, of which the area of arable land increased by 10.43 km\({}^{2}\), the area of forest land increased by 5.62 km\({}^{2}\), and the area of construction land increased most significantly by 48.74 km\({}^{2}\). However, from 2005 to 2015, the area of grassland and unused land showed a decreasing trend of 43.56 km\({}^{2}\) and 35.97 km\({}^{2}\), respectively. Water areas showed a trend of increasing and then decreasing, with an increase of 5.92 km\({}^{2}\) in 2005-2010 due to the increase in water conservancy facilities, and a decrease of 1.18 km\({}^{2}\) in 2010-2015, which was a small decrease and an insignificant change [22]. Although the  
Figure 1: Overview of the upper reaches of the Weigan River outlet.  
decrease in grassland and unused land and the increase in construction land are in line with the current situation of regional development, the increase in forest land is the result of the effective implementation of projects such as returning farmland to forest land and afforestation in recent years. However, it is undeniable that in addition to the impact of the rapid expansion of arable land and the significant reduction in grassland caused by the increasing exploitation of natural resources by human beings brought about by the rapid development of society, there are some parts of forest land and unused land in the study area that have been degraded by the effects of climate change.