| Arid climate is sensitive and vulnerable, and has obviously changed under global warming. In this paper, climate characteristics in three typical arid regions are analyzed, which are the ChinaMongolia arid region(CM)(75°E-105°E, 35°N-50°N), the Central Asia arid region(CA)(50°E-67°E, 28°N-50°N) and North Africa arid region(NA)(17°W-32°E, 15°N-32°N). The features of precipitation variation in annual and interannual, as well as abrupt change of precipitation have been analyzed in those regions. Subsequently, the relationship between precipitation and SST and circulation are discussed. What’s more, the changes of precipitation and water vapor transmission before and after the abrupt change year have also been discussed. The results indicate that there is more precipitation in summer in CM and NA, while precipitation in CA concentrates in winterspring mainly. This is the reason why these three arid regions are analysed here. The northwest arid region of China which is the main part of CM is also analysed. The results are summarized as follows.(1) Zonal water vapor transport is the main vapor source of arid zone in CM, the meridional water vapor transport is the main source of CA, but the vapor source of NA arid region comes either from the zonal or meridional moisture vapor transport which causes NA drought. During 1961-2010 net vapor transport has increased in CM(0.6×104Kg?s-1?10a-1) and NA(0.48×104Kg?s-1?10a-1) in winter, but it has decreased in winter CA(-0.62×104Kg?s-1?10a-1). Things are just contrary in this three regions in summer with the trend of-0.4×104Kg?s-1?10a-1 in CM,-0.23×104Kg?s-1?10a-1 in NA and 0.03×104Kg?s-1?10a-1 in CA. As net vapor transport has changed, annual, winter and summer precipitation have increased in CM, trend of which are 4.2mm?10a-1, 1.3mm?10a-1 and 1.0mm?10a-1. Both winter and summer precipitation have increased with the trend of 1.2mm?10a-1 and 0.1mm?10a-1, but annual precipitation has decreased in CA(-0.8mm?10a-1). Annual and summer precipitation have increased in NA with the trend of 0.3 mm?10a-1 and 1.0mm?10a-1, but winter precipitation hasn’t changed obviously.(2) General circulation from tropical to arctic can affect precipitation in arid regions through wave-current interaction. Winter precipitation in CM and CA are related to wave trains originated from Western Pacific Ocean and Indian Ocean. The winter precipitation in NA positively relates to wave trains of the North Atlantic. However, rainfall has a different response of SST in each chosen region. CM winter rainfall has a significant positive correlation(P>0.01) with West Pacific and Indian Ocean SST but the correlation turns insignificant in summer. The Central Asian rainfall relates to the Mediterranean and the Arabian SST, which always positive correlation to Arabian Sea but negatively related to the Mediterranean SST in winter and the correlation turns positive in summer(P>0.01). Further, rainfall has a certain relationship between the Mediterranean and the western Atlantic SST in NA(P>0.05).(3) Precipitation of northwest arid area has increased in each season, winter and spring precipitations increase significantly, summer and autumn rainfall increase insignificantly. Winter zonal net output has reduced, resulting in a total increase in water vapor transport in winter; the decrease of spring and autumn net zonal vapor input and the increase of summer net zonal vapor output causes the reduction of total water vapor input in spring, summer and autumn. The evaporation has increased significantly in the northwest arid areas, and the increasing rate in summer is the biggest. The vapor fluxes divergence decrease significantly, which mean the convergences become stronger, especially in the summer. Taken the effect of water vapor transport, evaporation and vapor convergence in consideration, the increasing of evaporation and convergence is the main positive driving force to precipitation in northwest arid area, but external vapor transportation can also affect the precipitation. As more water vapor transports into northwest arid area and the increase of evaporation in winter, the air moisture increases, and also the moisture convergence enhances, those result a significantly increase in winter precipitation. Though evaporation enhances in spring, the total water vapor input decrease, resulting in not obviously increase of moisture in atmosphere, with an enhanced vapor convergence precipitation increase significantly in spring. The enhancement of evaporation and moisture convergence also can’t offset the effect of the decrease of atmosphere moisture, summer and autumn precipitation increase insignificantly. |
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