1971-2010年西藏怒江流域冷暖冬的时空变化分析

根据暖冬等级国家标准,参照单站、区域暖冬等级标准,确定了单站和区域冷冬等级,在此基础上分析了1971-2010年西藏怒江流域9个站冷、暖冬事件的气候变化特征.结果表明:近40a怒江各站冬季平均气温表现出一致的增温趋势,增幅为0.31～0.77℃.(10a)-1,以那曲增幅最大,察隅升幅最小;1991-2010年气温快速上升为0.81～2.36℃.(10a)-1.在10a际尺度上,2000年代是近40a最暖期,与1970年代比较各站偏高1.0～2.5℃.区域暖冬指数也呈显著升高趋势,线性趋势为19.6%.(10a)-1,明显高于东北、华北、西北、华南等地.流域单站暖冬频率为40%～58%,强暖冬频率为15%～33%;区域暖冬共发生21次(年),主要出现在2000年代,其中强暖冬事件共发生过9次(年);2001、2006和2009年是过去40a中范围最广、强度最大的暖冬.流域单站冷冬频率为15%～28%,强冷冬频率为5%～13%;区域冷冬共发生了8次(年),以1990年代居多,其中区域强冷冬事件出现了4次(年);1983年是40a中范围最广、强度最大的冷冬,1978年次之.

Temporal-Spatial Changes of Cold and Warm Winters over the Nujiang River Basin in Tibet from 1971 to 2010

According to the China National Standards,the warm winter is classified into two groups by space and intensity grades.In the space group,the warm winter is divided into two spatial grads as single station warm winter,and regional warm winter.In the intensity group,there are two grades as weak warm winter(warm winter) and severe warm winter.Average winter air temperature is divided into 3 probability categories to define the threshold of warm winter for single station and its warm winter intensity.Then the division criterions for regional winter warm intensity can be calculated according to percentile rank of warm winter stations.In accordance with this standard,the grade of single station and regional cold winter are determined.On the basis of the division method for cold and warm winter,the characteristics of cold and warm winters from 1971 to 2010 over the Nujiang River basin in Tibet are analyzed.The results show that the mean temperature in winter has increased over the basin with a rate of(0.31~0.77) ℃·(10a)-1 from 1971 to 2010,with a maximum in Nagqu and a minimum in Zayü.However,after 1990 climate has warmed dramatically,with a temperature rising rate of(0.81~2.36) ℃·(10a)-1.Regional warm winter index has an obvious rising trend at a rate of 19.6 % per 10 years,which is higher than that in Northeast China,North China,Northwest China and South China et al.In terms of decadal variation,temperature was the warmest in the 2000s from 1971 to 2010,which was 1.0~2.5 ℃ more that in the 1970s.Frequency of single station warm winter was 40%~58%,with 15%~33% of severe warm winter.There were 21 regional warm winter years from 1971 to 2010,with nine severe warm winters,and the warm winter was mostly in the 2000s,while the most extensive and severe regional warm winter occurred in 2001,2006 and 2009.The results also show that the frequency of single station cold winter was 15%~28%,with 5%~13% of severe cold winter.There were eight regional cold winter years from 1971 to 2010,with four severe cold winters,and the occurrence of cold winter was more in the 1990s.Additionally,from 1971 to 2010,the most extensive and severe regional cold winter appeared in 1983,followed by 1978.