Clustering and Characteristic Analysis of Sub-daily Scale (< 12 h) Heavy Rainfall Types in South Korea Based on Observed Rainfall Data

In this study, we analyzed the spatiotemporal characteristics of heavy rainfall in South Korea over the past 10 years (2013–2022) using clustering methods on Hourly data from 398 observation stations. We derived 18 variables related to heavy rainfall to assess frequency and intensity over different accumulation times (1, 3, and 12 h). After optimizing stations (395), variables (17), normalization (Robust scaling), clustering method (K-means), and the number of clusters (4), we analyzed characteristics in terms of location, sub-seasonal variability, and diurnal variation among the clusters. In general, the detailed characteristics of the frequency and intensity of heavy rainfall in each cluster vary depending on the accumulation time. Cluster 1 (C1), located at most of inland areas excluding Gyeonggi-do, and C2, in the northern and Jeolla-do regions, have a wide range of occurrences but low heavy rainfall frequencies. Both clusters show relatively high frequencies in July and August and exhibit diurnal patterns with peaks in the early morning and afternoon. And C2 has double the frequency of heavy rainfall in July and August compared to C1. C3 is along the east and south coasts, showing peak frequencies and intensities in August and September with early morning diurnal peaks. C4, located in Jeju, Geoje, and Misiryeong, has the highest frequencies and intensities of heavy rainfall, peaking from June to September. C4, which is mainly located along the coast, has one early morning peak. The three observatories excluded from clustering, located in high-altitude areas of Jeju Island, experienced about four times more frequent heavy rainfall events than other clusters, but with slightly stronger intensity.