**2. Study Area**

The Tianshan Mountains are the mountain system that is the farthest in the world from any ocean. They are composed of a series of mountain ranges, intermountain basins, valleys, and piedmont plains, with an area of approximately 570,000 km<sup>2</sup> and an average altitude of 4000 m [4]. The precipitation distribution shows large temporal and spatial variations, with most precipitation occurring in summer and little occurring in winter. The Tianshan Mountains are also known as the water tower of central Asia. Approximately 65% of the rivers in Xinjiang originate from this region. On northern slopes, the annual average precipitation ranges between 500 and 700 mm, whereas the annual precipitation over western windward slopes can reach 1000 mm [23–25].
