Variations in water conservation function and attributions in the Three-River Source Region of the Qinghai–Tibet Plateau based on the SWAT model

The water conservation function is one of the important ecosystem services. Quantifying water conservation of the Three-River Source Region (TRSR) of the Qinghai–Tibet Plateau in China and its attribution are essential for maintaining the water needs of the local ecosystem and providing sufficient water resources to downstream countries and regions. However, there is a lack of comprehensive knowledge about the variations of water conservation on muti-temporal (annual, monthly) and spatial scales, and its attributions in land use/cover change (LUCC) and climate change (CC). In this study, the Soil and Water Assessment Tool (SWAT), a distributed hydrological model with flexibility, high adaptability, and explicit physical mechanism, was used to accurately estimate the water conservation of TRSR from 1981 to 2020, and then the attribution analyses were conducted on the TRSR and its three subregions of the Yellow River Source (YL), the Yangtze River Source (YTZ), and the Lancang River Source (LC). The results show that (1) The environmental changes including LUCC and CC in TRSR after 2000 were significant and dominated the overall trend. (2) The multi-year average water conservation in the TRSR was 65 mm and highest for the YL, followed by the YTZ, and lowest for the LC. Water conservation decreased initially and then increased, with an overall increase (0.94 mm/a). Water conservation increased by 45.3% in the later period, mainly occurred in the summer. The most significant increasing trend occurred in the YTZ, while LC was a key water conservation reserve. (3) CC dominated the increase in water conservation of TRSR with contributions of 83.5% where increased precipitation was the main reason. Increased evapotranspiration was responsible for water conservation reduction in most areas of the LC. (4) The effects of ecological measures were limited (accounted for 12.72%), but obvious in the YL (51.31%).