Climate Characteristics of Rainstorm in Hunan in the Last 37 Years

Based on daily precipitation of 97 meteorological observation stations in Hunan Province, statistical diagnostic analyses on annual rainstorm days and heavy rainstorm days over past 37 years (1981-2017) were performed by using several methods, such as linear trend analysis, EEMD (Ensemble Empirical Mode Decomposition). Results show that, generally, the spatial distribution of the annual-averaged rainstorm days had a decreasing trend from north to south, with two distinct high-value centers, one being in Nanyue Station (6.95 days of rainstorm and 1.19 days of heavy rainstorm), the other in Anhua and its surrounding areas (6.1 days of rainstorm and 1.16 days of heavy rainstorm). The lower values appeared in southwest part of Hunan, with the minimum center in Chengbu county (2.4 days of rainstorm and 0.11 days of heavy rainstorm). The rainstorm and heavy rainstorm days, intensities and their contributions to yearly rainfall had a increasing trend. Finally, the days of both rainstorm and heavy rainstorm had obvious 2-3 year and 4-8 year periodic variations, respectively, which tended to have an accelerating frequency in recent years.