Spatiotemporal Change of Spring Drought in Southwest China

A drought index analytical method based on a relative moisture index was used to evaluate meteorological data between 1958 and 2012 and study the temporal variation, spatial distribution, and sub-regional evolution characteristics of spring drought in Southwest China. The results showed a decreasing frequency of spring drought in the West Sichuan Plateau, Southwest Sichuan Upland, and Yunnan Plateau and an increasing frequency in the East Sichuan Basin and Guizhou Plateau from 1958 to 2012. In the first EOF model for spring drought intensity, the load vector fluctuated in equal phases of different areas. The main abnormal areas were the North Yunnan Plateau and Southwest Sichuan Upland. The second EOF model, distributed in opposite phases of the east and west, showed the characteristics of variances influenced by the atmospheric system. Four subregional abnormalities including the Yunnan Plateau, Guizhou Plateau, West Sichuan Plateau, and East Sichuan Basin were divided according to the load vector abnormality in REOF. The intensity of spring drought had a significantly increasing frequency in Jiangcheng and Ganzi, which had its mutation point from weak to strong appear in 1970a and 1975a, respectively. It also showed an increasing but not significant frequency in Anshun and Suining. The temporal fluctuating period was mainly 4 to 6a in the southwest during the recent 55a.