Abstract
Persistent extreme precipitation covering a large area usually causes severe flooding disasters in China, but how to depict it and what are the possible causes are still open questions. With Climate Prediction Center global unified gauge-based analysis of daily precipitation and NCEP/NCAR daily reanalysis dataset from 1979 to 2019, summer regional pentad extreme precipitation (RPEP) is defined according to the threshold of the 95th percentile of pentad precipitation with more than 5% land grids coverage in eastern China. While the definition of RPEP highlights the climate features of both the persistence and the regionality of extreme precipitation, it is distinctly different from the previous definitions that mainly reflect the synoptic aspects with daily data and have strictly temporal-spatial constraints. Four categories of RPEPs are objectively identified by K-means cluster analysis, i.e., South China (SC), South of Yangtze River (SYR), Jianghuai River (JHR), and North China (NC). Along the Yangtze River (SYR and JHR), intensity and area of RPEP are positively correlated with each other, and with the increase of RPEP intensity, its center of gravity tends to move eastward in all the four cluster regions and southward in Jianghuai River and North China, respectively, and vice versa. The RPEPs mostly persist for one pentad but can reach up to two to three pentads at most, and along with the duration of RPEP, its intensity and area are both enhanced accordingly. Furthermore, the frequency of RPEP increased significantly since the late 1990s in SYR, JHR, and SC. Associated with RPEP, strong pentad-mean convergence and ascending motion occur in the middle-lower troposphere, and except for SC that is dominated by the local low-pressure and cyclone anomalies, the other three cluster regions are all forced by the western Pacific subtropical high to the southeast and weak low-pressure trough to the north, and the low-level anticyclone anomaly to the southeast transports abundant water vapors to the RPEP regions accordingly. Besides, all the RPEPs are closely in accordance with obvious subseasonal oscillations, especially the 10–30-day and 30–60-day oscillations, which can be regarded as the potential sources of RPEP predictability in eastern China.
Highlights
At present, extreme weather and climate events are posing a serious threat to people’s life and health and are one of the important causes of natural disasters
To examine the climate characteristics of extreme precipitation from the aspects of extreme, persistence and regionality, the RPEP is defined with pentad precipitation that is greater than the relative threshold with more than 5% of total land grids in eastern China
All the authors contributed to the article and approved the submitted version
Summary
Extreme weather and climate events are posing a serious threat to people’s life and health and are one of the important causes of natural disasters. Regional extreme precipitation event is defined, which requires that precipitation is greater than or equal to 50 mm and lasts for at least five consecutive days or more, involving more than 10 grids (resolution 0.25 × 0.25°) in the region, wherein the coincidence rate of rainbands in the two adjacent days is not less than 20% (Wang et al, 2014) Another definition considers both the persistence and the regionality of daily precipitation; that is, daily precipitation amount must exceed 50 mm for at least three consecutive days and, at the same time, the distance of neighboring stations must be less than 200 km from each other (Chen and Zhai, 2013). Chen and Zhai (2013) found that most persistent extreme precipitation events occur in the central and southern parts of eastern China (primarily in the Jianghuai River basin and South China) and only a small fraction of them appear in northern China They are more frequent after 1990, with higher mean intensity, longer mean duration, and larger affected areas. Some RPEP metrics are defined to depict its characteristics: frequency is the pentad number of RPEPs at each grid; intensity refers to the ratio of the cumulative amount and frequency number of RPEPs at each grid; area ratio is the ratio between the number of grids with RPEP and the total land grids in research; location of the center of gravity is expressed based on the latitudes and longitudes weighted by the RPEP amount at each grid; duration is counted by how many consecutive pentads last in the RPEP
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