Changes in future drought characteristics in the Ili River Basin, China, using the new comprehensive standardized drought index

The construction of a comprehensive drought index and the evaluation of future drought characteristics are important for drought management decisions. In this study, we constructed a new comprehensive drought index (SWCI) that can comprehensively characterize the meteorological-hydrological-agricultural drought characteristics based on the hydro-meteorological factors (precipitation, evapotranspiration, soil water, surface runoff, and underground runoff, etc.) simulated by the VIC model coupled with the CMIP6 GCMs, and by using the D-Vine Copula function. Then, we applied the SWCI index to the Ili River Basin (IRB) and analyzed the change characteristics of comprehensive drought in the study area under the future climate change scenario. The results show that: (1) The spatial downscaling effects of CMIP6 and the runoff simulation effect of the VIC model were better during the historical period (1961–2014), which can provide reliable runoff and hydro-meteorological prognosis data, (2) The SWCI index comprehensively considers the hydro-meteorological factors closely related to the occurrence and evolution of drought, and can monitor the occurrence and development process of drought well. It can comprehensively describe drought characteristics from meteorological, hydrological, and agricultural perspectives, (3) The comprehensive drought intensity and duration decreased in the eastern basin (IRB1) under the SSP1-2.6 scenario. In contrast, the intensity and duration of the whole basin increased under the SSP2-4.5, SSP3-7.0, and SSP5-8.5 scenarios, with an average increase of at least 7.40 %, 2.14 %, and 13.78 %, respectively, and (4) The drought return period showed significant differences. In the historical period, the return period of moderate and above drought events (S > 1, P > 1, D > 3) in the IRB was longer. In the future period (2025–2078), the drought return period with S > 1, P > 1 and D > 3 was shorter than that in the historical period, with the greatest reduction in the southern (IRB2) and western (IRB3) of basin. Our results suggest that the comprehensive drought risk in the Ili River Basin will increase during the mid-21st century, and relevant defense preparations should be made for high-risk regions (IRB2 and IRB3).