Challenges of typical inter-basin water transfer projects in China: Anticipated impacts of climate change on streamflow and hydrological drought under CMIP6

Inter-basin water transfer projects are critical for economic development in water scarcity regions. However, the streamflow reduction and the frequent dry extremes in a warming environment raise significant concerns regarding the sustainability of such projects. Based on the latest CMIP6 data, hydrological model, Standardized Streamflow Index (SSI), and run theory, this study systemically examined the future streamflow and hydrological drought changes in the Hanjiang to Weihe River Water Diversion Project (HWWDP) area, China. Significantly, as the most challenging project management scenario, the response of spatially compound hydrological drought (i. e., concurrent hydrological drought in both the water intake and receiving area) was further revealed. This analysis offers the potential to yield novel insights into the prospective management strategies for the HWWDP. The investigation covers the baseline period (1971-2014) and future periods (2021-2100) under SSP245 and SSP585 scenarios. The outcomes demonstrate a decline in annual average streamflow of 5.0-6.4 (SSP245) hundred million cubic meters in the water receiving area and 4.6-7.5 (SSP245) and 3.4-8.1 (SSP585) hundred million cubic meters in the water intake area, respectively, compared to the baseline period. Furthermore, hy-drological drought frequency may increase in both the water receiving and source areas, particularly in the summer under SSP585. The duration, severity, and peak intensity of hydrological drought events in the receiving area are expected to exacerbate due to climate change, while those impacts on water intake area should be relatively minor. The spatially compound hydrological drought is expected to occur more frequently in different months except April. The conditional probabilities of spatially compound hydrological drought occurrence may rise by 5.2%-18.7% (SSP245) and 5.9%-20.4% (SSP585) in different months when drought occurs in the water intake area. Moreover, higher probabilities are expected to be observed from April to October when the water receiving area experiences drought. These findings underscore the necessity for adaptive climate change man-agement of the HWWDP to address the future reduction in streamflow and more severe hydrological drought.