Variations of summer precipitation in Tarim Basin and their linkages with the westerly, Asian monsoons and extratropical circulation

Precipitation plays an important role in the water resources system in Tarim Basin (TB), the most arid region in China. However, the source of water vapor for precipitation and its linkages with climate circulations still keep mysterious. Based on the observed precipitation of 21 stations from 1961 to 2020 in TB and the NCAR/NCEP reanalysis data, the temporal and spatial variations of summer precipitation in TB and their linkages with the westerly, Asian summer monsoons and extratropical circulation are investigated. The results show that: (a) the summer precipitation in TB changes consistently at all 21 stations, and exhibits an increasing trend (4.1 mm/decade) from 1961 to 2020 with large interannual fluctuations; (b) although the water vapor in TB mainly comes from the westerly circulation, the water vapor from the edges of Asians summer monsoons also plays an important role. It is unexpectedly found that the summer precipitation in TB is negatively correlated with the Westerly Index (WI). When the upstream westerly wind weakens, the northeast wind from the eastern boundary and the southwest wind from the southern boundary strengthen, which bring more water vapor from the edges of East Asian and South Asian summer monsoons respectively, leading to abundant precipitation in TB; (c) when the Eastern Atlantic/Western Russian pattern (EA/WR) is in extreme negative phase, there is an anticyclone anomaly near 55°N, 55°E, which weakens the upstream westerly wind and reduces the water vapor input of western boundary into TB. However, the water vapor input from the edges of the Eastern and Southern Asian summer monsoon strengthens, facilitating abundant precipitation in TB. This study provides a new insight into the joint influence of westerly, monsoons and extratropical circulation on summer precipitation in TB, which is meaningful for understanding the mechanism of change in summer precipitation and the trend projection of future water resources.