<p>Recently, due to the climate change, the frequency of extreme hydrological disasters such as drought and flood is increasing worldwide. Especially, sudden change in precipitation cause drought and flood often occur alternately in a short period of time, which is defined as a drought-flood abrupt alternation event. In this study, daily Standardized Precipitation Index (SPI) for the entire basin of South Korea is used to analysis the characteristics of the short-term abrupt alternation events of drought and flood, focusing on the short-term perspective rather than the monthly SPI. When the SPI value is less than –1.5 for 10 consecutive days, a drought event begins, whereas when the SPI value is more than 0.5 for 7 consecutive days, a drought event ends. On the contrary, when the SPI value is more than 1.5 for 10 consecutive days, a flood event begins, whereas when the SPI value is less than –0.5 for 7 consecutive days, a flood event ends. When the time interval between the end of drought event and the start of flood event is less than five days, a drought-flood abrupt alternation event is identified. The severity of drought-flood abrupt alternation event is defined similarly to the severity of drought using the SPI. We classified the severity into two types: SW(severity of whole period) and ST(severity of transition period). We used the additional statistical risk grade analysis. Nackdong River basin (southeastern region of Korea) has most severe grade of the SW rather than the other basins and the ST is lower than other basins. On the contrary, Yeongsan River basin (southwestern region of Korea) has most severe grade of ST rather than the other basins and the SW is lower than other basins. In conclusion, using daily SPI can determine the risk-prone areas through evaluating the frequency and severity of drought-flood abrupt alternation events. Due to climate change, increasing variability of precipitation, and frequent flood abrupt alternation events in the future, our results will cornerstone to predict the vulnerable and risk-prone region or preventing disasters.</p> <p><strong>Acknowledgement:</strong> This research was supported by a grant(2022-MOIS63-001) of Cooperative Research Method and Safety Management Technology in National Disaster funded by Ministry of Interior and Safety(MOIS, Korea).</p>