An Integrated Framework for Extreme Drought Assessments Using the Natural Drought Index, Copula and Gi* Statistic

Abstract

This study proposes a framework to evaluate extreme drought using the natural drought index, copula and hot spot analysis. The study area was South Korea. Data were used from 59 automatic synoptic observing system stations; the variable infiltration capacity model was used for the period from 1981 to 2016. The natural drought index was constructed from precipitation, runoff and soil moisture data, which reflect the water cycle. The average interval, duration and severity of extreme drought events were determined following Runs theory. The most extreme drought period occurred in 2014–2016, with 46 of the 59 weather stations exhibiting drought conditions and 78% exhibiting extreme drought conditions. The Inje and Seosan stations exhibited the longest drought duration of 6 months, the most severe drought was 5 times higher than the extreme drought severity threshold. The periods and locations of extreme drought were identified using the natural drought index corresponded to the historical droughts in South Korea. Furthermore, the joint return period of 50 years indicated the northeastern area of South Korea suffered from long-lasting and severe drought. Meanwhile, hot spot analysis was used to explore the extreme drought conditions and showed an increasing trend in the middle and northeastern parts of South Korea. Overall, this framework provides water resource managers with essential information about extreme events, extreme joint return periods, locations and significant trends of natural drought that have not been considered before.