Assessment of urban land use impacts on small-scale precipitation patterns during warm seasons: A case study of Japanese cities

In this study, we investigated the association between urbanization and extreme precipitation during hot seasons and examined the frequency and intensity of precipitation events exceeding predefined thresholds within several radii around three major Japanese metropolises, with the main radius set at 50 km. Our analysis used Radar-Raingauge Analyzed Precipitation data with a resolution of approximately 1 km. A distinguishing aspect of our study is the application of an image processing method to process planar precipitation data, thereby enabling the isolation of small-scale rain events and intense cores from large-scale precipitation events. Furthermore, numerical simulations were performed utilizing Markov chain Monte Carlo methods. Our findings indicate that extreme precipitation is generally more intense in urban environments compared to nonurban areas. Notably, this association is more pronounced for precipitation intensities exceeding 30 mm/h compared with those exceeding 10 mm/h. Additionally, we conducted local bivariate relationship analyses to assess the spatial relationships between urban land use and extreme precipitation, as well as between topography and extreme precipitation. With respect to urban land use, a potential positive correlation was observed in coastal urban areas, especially in the downwind regions of city centers; however, this varied depending on the terrain and location. These insights can inform urban planning efforts aimed at enhancing disaster prevention and promoting environmental sustainability.