Spatial correlations of regional tropical cyclone- and non-tropical cyclone-induced severe rainstorms during 2000 - 2019

Severe rainstorm is one of the most devastating disasters in southeast China (SEC). A deep and comprehensive understanding of the spatial correlations of severe rainstorms is important for preventing rainstorm-induced hazards. In this study, tropical cyclone- and non-tropical cyclone-induced severe rainstorms (TCSRs and NTCSRs) over SEC during 2000 - 2019 are discussed. Co-occurrence probability and range values calculated using semivariogram method are used to measure the spatial correlation of severe rainstorms. The extent to which potential factors (El Niño/La Niña, Indian Ocean Dipole (IOD), latitudes, longitudes, temperature, elevation, and radius of maximum wind) affect the spatial structure of severe rainstorms are discussed. The spatial correlation distances for TCSRs (300 - 700 km) in Typhoon season (July, August, and September) are longer than most of those for NTCSRs (150 - 300 km) in Meiyu season (June and July). The range values of TCSRs at each percentile (except for the minimum range values) tend to be omnidirectional. While NTCSRs tend to have the major direction of NE-SW. El Niño tends to increase the average spatial correlation distance of TCSRs in NE-SW and NTCSRs in N-NE. La Niña tends to decrease the spatial correlation distance of TCSRs in NE-SW. The occurrence of positive IOD and negative IOD (-IOD) events may increase the spatial correlation distance of TCSRs in NW-SE, and -IOD events may decrease the distance in NE-SW. IOD events especially -IOD may change the spatial correlation distance of NTCSRs in E-NE. Latitudes, longitudes, temperature, elevation, and radius of maximum wind significantly affect the spatial correlation distance of TCSRs in various directions.