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 important, because desertification is occurring in these regions. Even in the arid/semi-arid regions in the interior of the Eurasian Continent, heavy precipitation 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 interior region of the Eurasian Continent were investigated using the objective re-analysis data provided by the European Centre for Medium range Weather Forecast (ECMWF) for a five-year period (1980-1984). Through the analysis of the vertically integrated water vapor transporting mean summer fields, it is clarified that Mongolia and the northern part of China receive water vapor 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 of the water vapor is transported to the Taklimakan Desert from the northwest 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 Taklimakan Desert is one of the most arid regions in the Eurasian Inner Continent. Here, the daily mean water vapor flux patterns are classified using cluster analysis. The 460 maps prepared during the investigation are first classified into eight general patterns. Precipitation and atmospheric circulation patterns compositted by these clusters are then compared. Over 90 % of the total cases resemble the summer mean water vapor flux pattern, and northwesterly 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 simultaneous existence of a southwestward extending trough located to the north of this region, and the ridge located in Central Asia, is peculiar to the atmospheric circulation pattern of these cases. Although such situations appeared in up to 10 % of the total cases, they tend to occur mostly in the wet years (1981, 1984), and account for about half of the precipitation in those wet years.