Variations Of Dry-wet And Its Relationship With Water Vapor Transport In Northwest China During Recent 30a

With the ERA-interim reanalysis data, we calculated the climatology-average water vapor tr ansport in East Asia in spring, summer, autumn and winter respectively, and found that the North west China is mainly fed by two water vapor transport routes.One originates at Middle Asia and flows eastward to North China through northern Xinjiang. The other comes from Arabian Sea and then flows through Hindustan, the Bay of Bengal and Southwest China and at length arrives at the east part of the Northwest China and North China. Hereinafter, the two transport belt are called the northern branch water vapor transportation belt and the southern branch water vapor transportation respectively.We divide the Northwest China into the western and eastern part of the Northwest China, using the Longitude line of 103°E as the dilimitation of boundary. With the observations including temperature and precipitation datas we calculated the 12-month-time-scale SPEI in Northwest China. We analyze and discuss the inter-annual variation and inter-decadal variation of drought in the western and eastern part of Northwest China, and get the conclusion that:1) the annual drought in Northwest China has indistinctive periodical change in 2-5 and 20years; 2) the regional climate has experienced a interdecal shift around 1994, and the region tends to be wetter and wetter before 1994, while a trend toward drier appears after 1994.With the composite analysis, we found that 1)it is beneficial of the wetting in the western northwest China when the northern branch water vapor transportation belt is enhanced in spring, summer and winter; 2)it is beneficial of the wetting in the eastern northwest China when the northern branch water vapor transportation belt is reduced in winter and spring, enhanced in summer, and the stronger and near to the northern in summer and autumn of the southern branch water vapor transportation belt. The vapor transportation of the northern branch water vapor transportation belt in autumn and the southern branch water vapor transportation belt has no significant effect on the moist variation in the western northwest China. The vapor transportation of the southern branch water vapor transportation belt in winter and spring period has no significant effect on the moist variation in the eastern Northwest China. However, the significant decreasing of water vapor transportation after 1992 produced a positive influence to the dry-humid change mutation around 1994 in northwest China.