Analysis on Features of Regional and Continuous Drought in North Xinjiang in Spring and Summer

As a kind of climate disaster,drought causes big economic loss,especially the big agricultural loss,it is meanwhile known to be such a complex natural hazard and also much more severe than any other natural extreme events.As the most frequent and serious meteorological disaster in Xinjiang,drought is characterized by vast disaster area and long duration.Therefore,it attracts more and more attention of meteorologists to study drought.Precipitation in north Xinjiang,200 mm approximately,is much higher than that in south Xinjiang(about 50 mm),and utilization of the unified criteria to estimate the distribution of drought in these two distinguish regions is undoubtedly improper,so this paper focuses mainly on the variation of drought features in north Xinjiang(excluding the Tianshan Mountains).The previous researches focused mostly on seasonal change of drought,but few studies focused upon its regional and continual features.Complex topography induced dominantly the significant climatic difference between different regions and different seasons in north Xinjiang.Therefore,it is an issue worthy to lucubrate that how to analyze qualitatively the spatial features and time response of drought distribution.In this paper,the features of regional and continuous drought over the Junggar Basin in north Xinjiang in spring and summer were analyzed based on the daily precipitation data observed by 36 meteorological stations in Xinjiang during the period of 1961-2007.The results revealed that the extreme drought occurred most frequently in the basin,especially in northwest Xinjiang,where spring drought occurred every 3 years,but summer one occurred every 4-5 years.The probability of inter-seasonal draught occurrence was lower(10%),while the occurrence of inter-monthly continual draught was much more common,and the occurring frequency of 2-month continual draught was approximately 20% of the total.The analyzed results showed that the continual draught occurred most frequently in May and June in northwest Xinjiang.Spring draught was much more common than that of summer one in the Ili River Valley and north Tianshan Mountains as well as the northern part of north Xinjiang,and the extreme draught occurred most frequently in the north Tianshan Mountains.Draught intensity in the three regions was in a decrease trend.Spring drought frequency was low in the late-1990s,and summer one was low in the late-1980s.