Risk assessment of hydrological drought in water-donating and water-receiving areas of an inter-basin water diversion project.

Droughts are the most widespread natural disasters in arid/semi-arid regions, causing significant damage to socio-economic and agricultural systems. Inter-basin water diversion projects have been widely adopted to mitigate regional water scarcity. However, the dual impact of drought and water diversion on both water donating and receiving regions remains insufficiently explored. This study investigates the spatiotemporal evolution and risk of hydrological drought (HD) in the context of the Tao River Water Diversion Project (TRWDP) in Gansu province, China. By integrating hydro-meteorological datasets, SWAT-based hydrological modeling, and the Standardized Runoff Index (SRI), HD dynamics were assessed across both water-donating (TRB) and water-receiving regions (ZRB and WRB) from 1970 to 2020. Results indicate that: (1) HD exhibits a worsening trend, with the most pronounced intensification observed in the WRB. (2) Correlation analyses indicate that drought characteristics are driven by diverse climatic and catchment attributes. In the TRB, HD is primarily influenced by seasonal drought index, elevation variability, and proportion of water bodies; in the ZRB, by basin area, river network length, maximum elevation, and forest coverage; and in the WRB, by minimum elevation, river network density, and water area ratio. (3) A risk assessment framework integrating hazard, exposure, and vulnerability highlights critical drought hotspots in the lower TRB and central WRB. Notably, the implementation of the TRWDP has significantly alleviated drought risk in water-receiving regions, particularly in agricultural and densely populated areas. However, the potential redistribution of drought pressure toward water-donating regions underscores the need for balanced inter-basin water governance. These findings bridge the gap in understanding the interplay between water diversion and hydrological drought risk, providing a scientific basis for the adaptive management and sustainable operation of large-scale water transfer projects under climate variability.