A Spatial Cluster Analysis of Heavy Rains in China

Clustered heavy rains (CHRs) defined using hierarchical cluster analysis based on daily observations of precipitation in China during 1960-2008 are investigated in this paper. The geographical pattern of CHRs in China shows three high-frequency centers-South China,the Yangtze River basin, and part of North China around the Bohai Sea. CHRs occur most frequently in South China with a mean annual frequency of 6.8 (a total of 334times during 1960-2008). June has the highest monthly frequency (2.2 times/month with a total of 108 times during 1960-2008), partly in association with the Meiyu phenomenon in the Yangtze River basin. Within the past 50 years, the frequency of CHRs in China has increased significantly from 13.5 to 17.3 times per year, which is approximately 28%. In the 1990s, the frequency of CHRs often reached 19.1 times per year. The geographical extent of CHR has expanded slightly by 0.5 stations, and its average daily rainfall intensity has increased by 3.7 mm d-1. The contribution of CHRs to total rainfall amount and the frequency of daily precipitation have increased by 63.1% and 22.7%, respectively, partly due to a significant decrease in light rains. In drying regions of North and Northeast China, the amounts of minimal CHRs have had no significant trend in recent years, probably due to warming in these arid regions enhancing atmospheric convectivity at individual stations.