Diurnal Variability and Long-Term Changes in Extreme Summer Precipitation over South Korea

In this study, the diurnal characteristics and long-term changes of extreme precipitation over South Korea were investigated using hourly precipitation data from 59 Automated Synoptic Observing System (ASOS) stations for the 50-year period from 1973 to 2022. The analysis focused on the summer season (June–September), during which extreme precipitation events most frequently occur. Extreme precipitation events were defined using station-specific thresholds based on the 95th percentile of 3-hourly precipitation amounts during the early period (1973–1997).

During the early period, both the amount and frequency of extreme precipitation exhibited a pronounced maximum during the 01–09 LST period. In contrast, precipitation intensity showed two comparable maxima during 01–09 LST and 16–24 LST, with smaller diurnal amplitudes than those of precipitation amount and frequency. In the later period (1998–2022), a substantial increase in extreme precipitation amount and frequency was observed during the 04–12 LST period, accompanied by a shift in the timing of their diurnal maxima toward this time frame.

To better understand the mechanisms associated with extreme precipitation, the characteristics and changes of related atmospheric variables were also examined. During extreme precipitation events, a negative sea-level pressure anomaly was identified over western Korea, inducing southerly winds and positive moisture anomalies over southern Korea relative to the summer mean state. Compared to the early period, the later period exhibited increased atmospheric moisture and a higher frequency of moist conditions over South Korea. These moisture changes are likely associated with the enhanced extreme precipitation amount and frequency during the 04–12 LST period. In contrast, no statistically significant changes were found in the strength or frequency of southerly winds.