Copula-based construction of an integrated drought index in the Ba River basin, Viet Nam

Tóm tắt

Drought is a complex natural hazard characterized by stochastic occurrence, wide-ranging impacts, and sequential propagation across the hydrological cycle. This study proposes a copula-based framework to construct an Integrated Drought Index (IDI) for the Ba River Basin, Viet Nam, combining meteorological (SPI), agricultural (SMI), and hydrological (SRI, SGI) drought dimensions. The VIC distributed hydrological model was developed and calibrated for 1980-2023, explicitly incorporating the operation of major reservoirs to better capture regulated flow regimes. Standardized drought indices were computed at monthly timescales, and a Clayton Copula was applied to model lower-tail dependence among them, enabling quantification of compound drought conditions. The resulting IDI was analyzed for four representative drought years (2015, 2016, 2019, 2020), which correspond to major El Nino episodes associated with severe rainfall deficits and socio-economic damages. Results show that the IDI effectively captures both the intensity and spatial extent of drought propagation, with 2016 emerging as the most extreme basin-wide drought, 2020 showing similarly widespread impacts, and 2015 and 2019 characterized by more localized drought hotspots. By integrating reservoir regulation, multi-source data, and copula-based dependence modeling, this study provided a more holistic representation of compound drought risk in a socio-hydrologically complex basin.