Extreme hourly precipitation over China: Research progress from 2010 to 2019

This paper summarizes the research progress on extreme hourly precipitation (EXHP) over China in the past decade. The main results are as follows. (1) Thresholds of EXHP are usually defined using the percentile method or the empirical distribution function method. The thresholds of EXHP in China show substantial regional variations, with the most intense centers over the coastal South China, Hainan and Taiwan islands, and North China Plain, and two secondary ones in the Sichuan Basin and the middle-lower-reaches of the Yangtze River. (2) The EXHP records are classified into four types according to the synoptic situations under which they occur, i.e., the tropical cyclone, surface front, low-level vortex/shear line, and weak-synoptic forcing types. Each type presents distinctive characteristics in regional distribution and seasonal or diurnal variations. (3) An extreme hourly rainfall event (EXRE) is defined as a continuous time period with hourly rainfall rates at a station ≥ 0.1 mm·h^-1, with at least one EXHP record and at most 1 h intermittence. The average duration of EXREs exceeds 12 h in the southeast coastal regions and the Yangtze River valley, but is relatively short (< 6 h) in northern China. The rainfall evolution of EXREs is asymmetric, i.e., rainfall rates increase rapidly from the beginning of an event to the extreme value, but more slowly afterwards to the end of the event, especially over the complex terrains in western China. (4) Over the past 50 years, the positive trends of EXHP in China are scattered. Significant increasing trends of EXHP are observed in Shanghai megacity and the urban cluster over the Pearl River Delta during the rapid urbanization period, which differ from their surrounding areas. Both the observation and modeling studies suggest that the strong urban heat island effect in Beijing is conductive to intensification of hourly precipitation.