Assessment of water retention variation and risk warning under climate change in an inner headwater basin in the 21st century

Identifying the dynamics of water retention (WR) is critical for developing adaptive strategies for effective water resources management under climate change. However, our understanding about the responses of WR to climate change is still limited, which hinders risk assessment and warning of WR under future climate trajectories. In this study, we used the Soil and Water Assessment Tool (SWAT) to quantify the impact of climate change on WR in the upper Heihe River Basin (UHRB), a typical inner headwater basin, and predicted the future trends and po-tential degradation risks of WR based on climate scenarios under three Representative Concentration Pathways (RCP2.6, RCP4.5, and RCP8.5). Our results showed that the historical (1971-2020) average WR in the UHRB was approximately 91.1 mm, with high WR occurring in the middle and west of the basin and low WR in the north and southeast. Our prediction suggested that the WR may remain stable during the near future (2021-2060) under the RCP2.6 scenario; however, WR may decrease by 23 % and 32 % during this period under the RCP4.5 and RCP8.5, respectively. By the end of this century (2061-2099), the WR may decrease by 10 %, 40 %, and 69 % under the RCP2.6, RCP4.5, and RCP8.5 scenarios, respectively, due to the substantially enhanced evapo-transpiration in the warming context, though a slight increase in precipitation may partly offset this negative impact. In brief, this study provides a paradigm for assessing the dynamics and future degradation risk of water retention at watershed scale, and this can be valuable and applicable for other areas.