中国西北地区近700年来夏季干湿变化特征

The characteristics of summer moisture variations over northwest China during the past 700 years

基于观测数据得到的帕尔默干旱指数(Dai-PDSI)和树木年轮重建的帕尔默干旱指数(MADA-PDSI),分析了中国西北干湿分布及变化特征.通过对1951-2005年夏季Dai-PDSI数据的REOF分析,可将中国西北地区划分为3个典型干旱区:南疆干旱区、北疆干旱区和西北东部干旱区.区域平均PDSI分析结果表明,自1951年以来,南疆呈现出明显的变湿趋势,北疆地区先变干后转湿,而西北东部干旱化趋势明显.近700年来的相似干旱期的分析结果显示,各类型相似干旱期都有其共性,南疆相似干旱期的主要特点是干旱从西北向东南延伸到长江中下游地区,北疆相似干旱期的严重干旱位于北疆及其北部地区,而西北东部干旱发生时中国大部分地区遭遇干旱,且严重干旱位于北方地区.20世纪以来的南疆和北疆干旱在历史时期中都有与其强度相当的相似干旱期,而西北东部历史相似干旱期与1995-2005年干旱相比,其干旱强度相对较弱,因此,1995-2005年干旱是此类型近700年来最严重的干旱.

The Northwest China is one of the most arid regions in the middle latitudes, where water is scarce all the year round. The variations of summer moisture in this region were investigated using the palmer drought severity index （PDSI） derived from instrumental data （Dai-PDSI） and tree-ring records （MADA-PDSI）. Based on the rotated experience and the orthogonal function （REOF） analysis of summer PDSI in the northwestern China during 1951- 2005, there have been three main drought regions： the southern and northern parts of Xinjiang and eastern part of Northwest China. The area-averaged PDSI indicated a wet tendency in the southern part of Xinjiang, and a dry-wet tendency in the northern part of Xinjiang since 1951; on the contrary, the eastern part of Northwest China showed a clear tendency to be dry. An analysis of similar drought periods during the past 700 years by using MADA-PDSI showed that the similar drought periods in each region shared some common characteristics. The main characteristic of the southern part of Xinjiang drought was that it would extend from Northwest to Southeast China. Serious drought was also located in the northern part of Xinjiang and areas even north of it. When drought occurred in the eastern part of Northwest China, most areas in eastern and northern China would also suffer from dry weather. Drought in the northern and southern parts of Xinjiang during the 20 th century have had a similar pattern and intensive drought periods also happened in history. Because of its strong intensity, the drought during 1995-2005 was the most serious in the eastern part of Northwest China, though similar severe droughts also occurred in history.