Variation characteristics of drought and influence risk assessment for the main growing areas of winter wheat in Gansu Province during 40 years

rought is the main meteorological disaster affected winter wheat growing in Gansu Province. Using the data of precipitation and winter wheat yield from eight weather stations of counties during 1971 to 2010 which located in main growing areas of winter wheat in Gansu Province, has analyzed the spatial and temporal variation characteristics of drought during 40 years, set up the risk assessing index for drought disaster impacted to the winter production, carried out the analysis and evaluation to the risk of different grade of drought for the winter wheat in different season. The results showed that: The highest frequency of drought in spring was occurred in the Longdong loess plateau, as 0.35 to 0.39 times per year; the least frequency in the Huicheng Bas in and Liangjiang Rivers Basin, as 0.18 times per year. The highest frequency of drought in early summer was occurred in Huan County, as 0.35 times per year; the least frequency in Xifeng City, Cheng County and Qinan County. The highest frequency of drought in hot summer was occurred in Huan County and Maiji District, the least frequency in Zhangjiachuan. The highest frequency of drought in autumn was occurred in Huan County, the least frequency in Wudu City. The major draught disaster was the light drought in each region, the secondly drought disaster was the middle drought. During the 40 years, the most frequency of drought was occurred in 1990 s, but the least in 1980s.The trend of drought frequency in autumn has significantly decreased and in spring relatively increased since into 21st Century. The minimal influence risk by drought in whole growth season of winter wheat was the Huicheng Basin and Liangjiang River Basin with the maximal planting insurance rate as 92% to 93%; The secondly was the Guan Mountain Areas with the planting insurance rate as 91% and less influence risk by drought; The larger drought risk was in the Weihe River Basin and Weibei Arid Area with the planting insurance rate as 88% to 89%; The minimal planting insurance rate was in Longdong Loess Plateau as 83% to 85%, the winter wheat growth was suffered the maximal drought stress.