Spatiotemporal evolution characteristics of meteorological and hydrological drought in Hengjiang River Basin under climate change

Abstract

[Objective] To analyze the spatiotemporal variations of meteorological and hydrological droughts in the Hengjiang River Basin under climate change, and to inform drought mitigation and water resource management. [Methods] Four CMIP6 climate scenarios(SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5) under the CMIP6 framework were selected, and the Soil and Water Assessment Tool(SWAT) model was applied to estimate runoff in the Hengjiang Basin. Based on the standardized precipitation index(SPI), standardized runoff index(SRI), and Copula function, the joint distribution characteristics of meteorological and hydrological droughts in the Hengjiang River Basin during the historical period(1980—2014) and the projected period(2015—2100) were analyzed. [Results] The SWAT model demonstrated strong applicability in the Hengjiang River Basin, with calibration and validation result showing R², NSE, R_e values of 0.91, 0.90, and-0.01(calibration), and 0.96, 0.89, and 0.13(validation), respectively. During the historical baseline period(1980—2014), the river basin exhibited an intensifying trend of meteorological and hydrological droughts, with annual average precipitation and runoff decreasing simultaneously. The annual average SPI and SRI values approached mild drought levels(-0.44). The frequencies of severe and mild meteorological droughts increased across the river basin, while the frequencies of moderate to severe hydrological droughts significantly rose in most regions, accompanied by occasional extreme drought events. During the projected period(2015—2100), precipitation and runoff were projected to increase significantly, leading to an overall alleviation of meteorological and hydrological droughts. The frequency of mild meteorological droughts was expected to increase significantly, while the frequencies of moderate and severe meteorological and hydrological droughts were projected to decrease substantially. However, the frequency of extreme meteorological and hydrological drought events was anticipated to increase. In the Hengjiang River Basin, short-term drought risks(return period <2 years) would decrease, with meteorological and hydrological drought intensities tending to converge. However, in the long term(return period >10 years), the lagged response of hydrological drought to meteorological drought was expected to intensify. [Conclusion] In the future, the Hengjiang River Basin is projected to become increasingly humid, with both meteorological and hydrological droughts alleviated. Therefore, while addressing meteorological and hydrological droughts in this river basin, measures should also be strengthened to address the trend toward increased humidity, enhance water resource planning and management capabilities, and improve flood control and waterlogging prevention capacities.

Keywords

meteorological drought / hydrological drought / Copula function / SWAT model / drought evolution / Hengjiang River Basin / basin water resources / influencing factors