Assessment of environmental ecological drought using environmental flow-based indices and copula analysis in an urban tributary of South Korea

초록

This study presents a copula-based bivariate modelling framework to quantitatively assess meteorological and environmental ecological droughts in the Tan River Basin, South Korea. Two indices-the Environmental Ecological Flow Index (EI) and the Standardized Precipitation Index (SPI)-were integrated to analyze drought duration and severity using 15 years of hydrological data (2009-2023). The Gaussian copula provided the best fit for SPI, whereas the Gumbel copula was optimal for EI. Nine meteorological (SPI-based) and 26 ecological (EIbased) drought events were identified. The most severe events occurred in 2015-2016 and 2016-2017, with return periods of 13.9 and 15.9 years, respectively. Joint return period analysis revealed strong dependence between duration and severity, with ecological droughts showing longer persistence and delayed recovery. The proposed copula-based framework effectively captures drought propagation from meteorological to ecological scales and supports integrated modelling for eco-hydrological assessment and sustainable water resource management.

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