Impacts of tropical cyclones on summertime short-duration precipitation extremes over the middle-lower reaches of the Yangtze River valley

Abstract

This study investigated variations in summertime short-duration precipitation extremes over the middle-lower reaches of the Yangtze River valley (MLYRV) and the possible impacts of tropical cyclones (TC) on these changes over the 1961–2016 period. Three short-duration precipitation types, including all events and the events in the 75th and 95th percentiles, are defined. At the 75th percentile, both the amount and number of TC-induced extreme short-duration rainfall events exhibit slightly declining trends, and the trends are not pronounced for the 95th-percentile cases. The number and amount of TC-induced 95th-percentile events are approximately one order of magnitude larger than those of the 75th-percentile cases, indicating that TCs play a more significant role on the upper tail of the rainfall distribution over the MLYRV in summer than on the rest of the precipitation distribution. A large number of the defined non-TC precipitation events are mainly distributed over the central-south MLYRV and southeastern regions. The spatial patterns of TC-induced rainfall resemble the contributions of TC-induced precipitation events to the total summer rainfall, with large values located in southeastern regions of the MLYRV. The spatial distribution of 95th-percentile events is principally attributed to the frequency of TC activities and to the TC tracks. Most of the TCs that trigger 95th-percentile events make landfall over the southeast MLYRV, and the corresponding large frequency of TC tracks is mainly situated over the ocean to the east of Taiwan. Both environmental factors and atmospheric circulations modulate the variations in extreme short-duration rainfall events. In particular, equatorward displacement of the western Pacific subtropical high impacts TC track density, resulting in more occurrences of precipitation extremes in 95th-percentile events over the MLYRV.