The Spatial and Temporal Characteristics of China Continuous Cold Rainy Weather and South Cold Damage from February to May

Based on observed daily temperature and precipitation data of China 546 observation stations and daily sunlight hours of some representative stations in spring rice producing regions from 1951 to 2007, a uniform standard for continuous cold rainy weather all over China and cold damage of spring rice producing regions is defined. Temporal and spatial characteristics are also summarized using some statistical methods, for example, Empirical Orthogonal Function Decomposition (EOF) and Morlet wavelet analysis. The results show that usually more continuous cold rainy weather occur in the regions of Sichuan Basin, Guizhou Province, western parts in the south of the Yangtze and South China during the period of February to May. The maximum occurring in Sichuan Basin and Guizhou Province reaches up to 4-6 days per spring month averaged from 1951-2007. The scope of continuous cold rainy weather gradually expands northward and westward from the south of the Yangtze to the Yellow River Basin in spring, in which obviously continuous cold rain weather occurs in the southeastern parts of Northwest China and the southeastern Tibet since March and in Northeast China in May. The decadal changes of the continuous cold rainy days in spring denote that there are less days than climate average during the 1950s and from 1997 to present, and the temporal variations of the first EOF mode of the continuous cold rainy days of China show the characteristics of decade oscillations including inter-month seesaw during the period of 1963-1996.The spatial and temporal characteristics of cold damage for China spring rice producing regions during the period of 1951-2007 show that the frequency of cold damage occurring in Sichuan Basin and mid-lower Reaches of the Yangtze are once in every 1.5 years, more than that of the northern and southern parts of South China with once in every 2.5 years, where severe cold damage occurs frequently in Sichuan Basin and mid-lower Reaches of the Yangtze but the frequencies of moderate and severe cold damages are equivalent in the northern and southern parts of South China. The analyses also show that 3-4 years significant oscillation period of cold damage exists in the aforementioned 4 spring rice producing regions and moreover, a significant decadal oscillation of cold damage exists in Sichuan Basin. In 4 spring rice producing regions, there have been less cold damages since 2000. Moreover, cold damages are excessive and severe during the period of 1990s except for the northern of South China regions.