GEV-based Extreme Precipitation in Summer Over the Korean Peninsula for 1973–2024

Understanding long-term trends in summer extreme precipitation is crucial for disaster risk management and climate adaptation. Yet, differences between hourly and daily extremes, as well as discrepancies between station-based observations and reanalysis data, are not fully explored. Here, we analyze summer precipitation (June–August) over the Korean Peninsula during 1973–2024 using ASOS observations and ERA5 reanalysis. Extreme precipitation is characterized by applying the generalized extreme value (GEV) distribution for daily (RX1DAY) and hourly (RX1H) maxima, and change point detection is applied to evaluate temporal nonstationarity in extreme precipitation characteristics. While mean JJA precipitation and RX1DAY show modest increases over 52 years, with the former rising by about 10.3% (0.79 mm/day) and the latter by approximately 11.4% (13.90 mm), RX1H exhibits a statistically significant increase of 19.6% relative to its climatological mean (p < 0.01), indicating a stronger intensification at shorter timescales. Additional analysis shows that this intensification is not strongly linked to station elevation, suggesting a limited role of local topography in the temporal evolution of short-duration extremes. ERA5 substantially underestimates extremes, by up to about 2.5 times for RX1DAY and about 4.9 times for RX1H, with biases becoming more pronounced at shorter temporal scales. Despite these magnitude discrepancies, ERA5 broadly reproduces the large-scale spatial patterns of extreme precipitation, indicating its usefulness for regional-scale diagnosis while highlighting limitations in quantifying localized extremes. Spatial patterns reveal enhanced daily return values along the Taebaek Mountains, southern coasts, and Jeju Island, whereas hourly return values exhibit more complex and localized inland distributions. Return-period analysis indicates that several stations have already experienced events exceeding the 200-year return period for both RX1DAY and RX1H. Change point detection identifies 1994 as a key transition year for RX1H, after which the both intensity and frequency of short-duration extreme precipitations increased markedly. This regime shift is consistent with previously reported decadal-scale changes in the East Asian summer monsoon circulation, suggesting that large-scale dynamical changes, together with thermodynamic amplification, have contributed to the intensification of hourly extremes. Overall, summer extreme rainfall in South Korea has intensified over the past five decades, becoming increasingly concentrated at shorter timescales. These results underscore the importance of long-term station observations for robust estimation of short-duration extremes, while emphasizing the escalating risks under climate change and the need for improved representation of localized extreme precipitation in reanalysis products and climate models.