Research on hydrological drought trends in water source area of South-to-North Water Diversion Middle Route Project under different climate scenarios

Abstract

[Objective] Future evolution of hydrological drought in the water source area of the South-to-North Water Diversion Middle Route Project under climate change is quantified, providing a basis for the security management and scheduling optimization of water resources for the project.[Methods] Downscaled data under the SSP1-2.6, SSP2-4.5, and SSP5-8.5 scenarios from the CMCC-ESM2 model in CMIP6 were used to drive the SWAT model to simulate the runoff processes in the water source area for the future period(2026—2100). The Mann-Kendall trend test and the annual-scale standardized runoff index(SRI) were applied to identify evolution trends of runoff and hydrological drought.[Results] Compared with the baseline period(1970—2020), the future multi-year average runoff in the water source area showed an increasing trend under different climate scenarios, and the magnitude of increase expanded as radiative forcing intensified. The upper-reach Hanzhong station exhibited the most pronounced increase and trend significance, while the runoff increment was most notable at the downstream Baihe station. Significant spatial heterogeneity was observed in the future hydrological drought across the water source area. Under the SSP1-2.6 scenario, the drought frequency in the middle and lower reaches decreased to 0.33~0.45, and the drought severity was reduced compared with the baseline period. Under the SSP2-4.5 and SSP5-8.5 scenarios, the drought frequency in the upper reach increased to 0.40~0.45, and the maximum increases in drought duration and severity at the Ankang station reached 22.1% and 23.4%, respectively.[Conclusion] The water source area exhibits pronounced spatial differences in its response to climate change. Under low-to-medium emission scenarios, Hanzhong and Baihe stations are characterized by a “high-frequency, short-duration, and low-severity” pattern. Under high-emission scenarios, droughts in the middle and lower reaches tend to become more persistent and intense, imposing greater demands on water resource allocation and drought mitigation in the future for the Middle Route Project.

Keywords

South-to-North Water Diversion Middle Route Project / SWAT model / Delta downscaling / CMIP6 / hydrological drought / climate change / runoff / water resource security