Where does the runoff come from in dry season in the source region of the Yangtze River?

Abstract

The present study focuses on the recharge source of the runoff of dry season based on the runoff change, stable isotopes and hydrochemical characteristics evidence in the source region of Yangtze River. The results showed that the runoff showed a significant increasing trend from 1956 to 2018 and the runoff increased by 21.5 m3/s·10a (Zhimenda station (ZMD)) and 40.0 m3/s·10a (Tuotuohe station (TTH)), especially in dry season. Moreover, the hydrogen and oxygen isotopes in dry season was more positive than that in wet season in the source region of Yangtze River. The main source of runoff in dry season is mainly affected by precipitation, supra-permafrost water and soil water in summer. Meanwhile, atmospheric precipitation, supra-permafrost water and soil water had a great impact on the recharge and the stable isotope characteristics of runoff of dry season. Furthermore, the hydrochemical type of runoff of dry season was similar as that for supra-permafrost water. Whether from the stable isotope or hydrochemical characteristics, it provides us with an idea that the main source of runoff of dry season is supra-permafrost water. Through the further analysis of recharge mode and recharge ratio of runoff of dry season, the major recharge sources of runoff of dry season is precipitation in autumn (TTH:58%, ZMD:61%). Moreover, the recharge patterns of runoff of dry season were direct recharge and indirect recharge. The subsequent findings could provide an overall understanding of the variational characteristics, causes, and sources of runoff of dry season and its hydrological effects in cold regions.