Abstract. In the middle and lower reaches of inland river basins of arid regions, human-intensive exploitation directly determines the distribution patterns of plants in arid areas and further determines the patterns of water use and the water cycle in arid regions. However, human activities on vegetation water utilization and the influence of the water cycle process and mechanism are not clear. In this study, seven observation systems were set up to collect samples in the mountainous, oasis and desert areas of the Shiyang River Basin, an arid inland river in central Asia. In order to quantitatively assess the contribution of different potential water sources to plants, stable isotopes of various water bodies in different geomorphic units of the basin were analyzed. The results showed that precipitation and soil water were the main sources of forest trees in mountainous areas, and the farmland vegetation in the middle and lower reaches of the oasis mainly absorbed soil water supplied by irrigation. The desert area forms vegetation in the ecological water transport area, and vegetation mainly absorbs soil water, lake water and groundwater formed by ecological water transport. On the whole, the water use patterns of plants in mountainous areas are not affected by human activities fundamentally, the oasis area is mainly affected by irrigation activities, and the inland river terminal lake area is mainly affected by ecological water transport. Human activities determine the water use patterns in the middle and lower reaches of inland rivers in arid areas.

Abstract. Mountainous areas are the main water-producing and source areas of rivers. Global climate change is transforming the distribution of plants and forms of water use. Therefore, a clear understanding of evapotranspiration in mountainous forest zone is key for understanding the ecohydrological effect of vegetation and its influence on the water cycle of the watershed. We quantified the evapotranspiration processes in the forest belts of the Qilian Mountains as well as their contribution to runoff yield and concentration based on precipitation, soil water, and plant water samples and experimental data. The study showed that transpiration of Qinghai spruce accounted for the highest proportion of evapotranspiration in the entire Qinghai spruce forest ecosystem, with an average of 79 %, which means that transpiration is much greater than evaporation. Soil water content and air humidity were the dominant factors influencing evapotranspiration in Qinghai spruce forest belts. The growing season of Qinghai spruce is characterized by greater evapotranspiration than precipitation in each month. Consequently, the forest zone does not yield flows in the eastern part of the Qilian Mountains. The warming of global temperatures and human activities are likely to trigger shifts in the distribution areas and evapotranspiration regimes of Qinghai spruce, which in turn will lead to a change in water resource patterns in the basin.