Monitoring and Evaluating the Severity of Drought-flood Abrupt Alternation Events Using Daily Standardized Precipitation Index

Abstract

A drought-flood abrupt alternation (DFAA) event is an extreme combination of an overlapping drought and flood resulting in adverse impacts on ecosystems and human society. As precipitation variability increases due to climate change, the occurrence and magnitude of DFAA events are expected to increase. Using daily precipitation data for 1966–2018, we calculated the daily standardized precipitation index for middle-sized watersheds and evaluated the severity of DFAA events in South Korea. The severity of DFAA events was evaluated in two ways: the severity of whole period (SWP) represents the total magnitude of DFAA event, and the severity of transition period (STP) indicates the instantaneous severity of DFAA event during the transition from drought to flood. The severities were also graded by the quantiles to identify risk regions, and we used precipitation concentration degree (PCD) and precipitation concentration period (PCP) to analyze the relationship between DFAA events and precipitation trends in South Korea. The results showed that the STP in the Yeongsan River basin and SWP in the Han River and the Nakdong River basin were higher than in the other basins. In addition, considering patterns and trends of the PCF and PCP in South Korea, this study found that the frequency and severity of DFAA events were high during flood seasons when precipitation was concentrated.