Variation of summer water vapor transport related to precipitation over and around the arid region in the interior of the Eurasian Continent

The variability of the hydrological cycle for arid/semi-arid regions is imp ortant, because desertification is occurring in these regions. Even in the arid/semi-arid regions in the interior of the Eurasian Continent, heavy pre cipitation sometimes occurs. However, the relationship between water vapor transport and precipitation has not been clarified yet. In this study, water vapor transport and flux divergence in the arid interi or region of the Eurasian Continent were investigated using the objective r e-analysis data provided by the European Centre for Medium range Weather Fo recast (ECMWF) for a five-year period (1980-1984). Through the analysis of the vertically integrated water vapor transporting mean summer fields, it i s clarified that Mongolia and the northern part of China receive water vapo r from the northwest. One of the water sources for these regions is located over, and to the west of Western Siberia. In the lower troposphere, most o f the water vapor is transported to the Taklimakan Desert from the northwes t along the eastern periphery of the Tianshan Mountains in the mean summer state. The daily summer water vapor flux fields around the Taklimakan Desert for a five-year period were analyzed in relation to precipitation there. The Tak limakan Desert is one of the most arid regions in the Eurasian Inner Contin ent. Here, the daily mean water vapor flux patterns are classified using cl uster analysis. The 460 maps prepared during the investigation are first cl assified into eight general patterns. Precipitation and atmospheric circula tion patterns compositted by these clusters are then compared. Over 90 % of the total cases resemble the summer mean water vapor flux pattern, and nor thwesterly moisture flows prevail. We found that the southerly water vapor flows, which pass over the Tibetan Plateau and along the eastern periphery of the Plateau in the lower level, are related to heavy precipitation over the Taklimakan Desert. The simultan eous existence of a southwestward extending trough located to the north of this region, and the ridge located in Central Asia, is peculiar to the atmo spheric circulation pattern of these cases. Although such situations appear ed in up to 10 % of the total cases, they tend to occur mostly in the wet y ears (1981, 1984), and account for about half of the precipitation in those wet years.