Contribution of cryosphere to runoff in the transition zone between the Tibetan Plateau and arid region based on environmental isotopes

Abstract. As the transition zone between the Tibetan Plateau and the arid region, the Qilian Mountains are important ecological barriers and source regions of inland rivers in northwest China. In recent decades, drastic changes in the cryosphere have had a significant impact on the quantity and formation process of water resources in the Qilian Mountains. In this study, 2164 environmental isotope samples were used to quantify the runoff components of 11 major rivers in the Qilian Mountains and to investigate the influence of cryosphere changes on mountain runoff. The results showed that the mountain runoff mainly comes from the cryosphere belt, which contributes to approximately 82 %、71 %, and 80 %, respectively, in the Hexi inland water system, upper stream of the Yellow River system, and Qinghai inland river system; the remaining amounts are contributed by precipitation in the vegetation belt. The maximum contribution ratio of glacier and snow meltwater to runoff occurred in May, but not in July and August, when the temperature was the highest. The important contribution of supra-permafrost water to runoff gradually increased from May to October and reached approximately 40 % in some rivers in October. Cryosphere degradation in the Qilian Mountains after 90 years has caused a rapid increase in runoff, a change in the peak runoff time, and an increase in runoff in winter. These changes in hydrological processes bring opportunities and challenges to managing inland river water resources, and various adaptive measures to seek advantages and avoid disadvantages have been proposed. The findings from environmental isotope analysis provide insights into realizing harmony of life, agriculture, industry, and ecological water use.