# Recent Spatiotemporal Changes of Subhourly Extreme Rainfall Events in Seoul
## 1 Introduction  
In recent decades, South Korea has made substantial efforts toward flood defense, achieving minimal flood damage from rainfall events with a frequency of less than 100 years. These efforts have primarily targeted fluvial flooding, as evidenced by the construction of levees and dams along major rivers. Although damage from fluvial flooding has significantly decreased, fluvial flooding has become more prevalent because of climate change. For example, Seoul has experienced sporadic urban flooding, with notable incidents occurring in 2010, 2011, 2018, and 2022. Over the past 15 years, flooding has affected the city approximately 25% of the time. As Seoul is South Korea's capital, even minor flooding there can result in considerable economic damage. To mitigate the effects of urban flooding and devise effective future strategies, comprehensive investigations and analyses of the current patterns and characteristics of extreme rainfall events are essential. Such efforts will significantly enhance our understanding of extreme rainfall phenomena in Seoul. Extensive research has been conducted on the temporal and spatial changes in rainfall characteristics owing to climate change [1, 2, 3, 4]. Numerous studies have specifically examined the impact of climate change on rainfall patterns in South Korea. For example, [PERSON], et al. [5] identified a statistically significant trend of increasing annual maximumprecipitation (AMP) in certain regions of South Korea. Although the increase in AMP was not statistically significant, trends showing an increase in probable rainfall values have also been observed [6]. Additionally, some studies have investigated the spatial and temporal changes associated with climate change across various variables, including drought and soil erosion [7; 8; 9; 10; 11]. Many studies have focused on large geographic areas rather than smaller urban areas when analyzing rainfall patterns. Urban flooding is typically evaluated through simulations using rainfall data rather than direct surface water observations because of the intermittent nature of these events [12; 13; 14]. Generally, high-resolution spatiotemporal rainfall data are essential for effectively assessing and analyzing the impact of urban flooding [15]. However, a lack of long-term high-resolution rainfall data, particularly in South Korea, has resulted in a deficiency in studies on urban flooding and its effects in the context of climate change. To prevent urban flooding and mitigate the damage from urban inundation, it is crucial to investigate the spatiotemporal variations in urban flooding. Therefore, examining the spatiotemporal variations of rainfall patterns in urban areas based on high-resolution data is required to achieve these goals. This study aims to examine the spatiotemporal changes in extreme rainfall in Seoul based on subhourly rainfall data derived from an extensive observation network. It attempts to address the following hypotheses to improve our understanding of extreme rainfall events in Seoul:  
1. Temporal characteristics of extreme rainfall in Seoul have changed. 2. Spatial patterns of extreme rainfall in Seoul have been altered. In the current study, the spatial patterns refer to the dispersion and autocorrelation of AMPs. The dispersion and autocorrelation represent the spatial clustering of AMPs. The temporal characteristics of extreme rainfall indicate trends in AMP series and spatial patterns. Temporal trends in the extreme rainfall time series were analyzed using the Mann-Kendall trend detection (MK) test, while the spatial patterns of extreme rainfall events in Seoul were examined based on the coefficients of variation (CV) and [PERSON]'s \(I\). It was assumed that the spatial pattern of extreme rainfall had changed when temporal trends in CV and Moran's \(I\) were detected. This study's findings will help us better understand the variations in extreme rainfall in Seoul, particularly in urban areas of South Korea. This will enhance our capacity to mitigate and prevent urban flooding and inundation.