Why has the summer rainfall increased prominently in the West Tarim Basin of Northwest China since 2010?

Abstract

Based on the monthly rainfall data at 32 weather stations located in the periphery of the Tarim Basin in Northwest China, which can mostly represent the rainfall variations in the whole basin, provided by the China Meteorological Data Network and the reanalysis data provided by the NCEP/NCAR during 1961–2021, the changes in summer rainfall in the Tarim Basin and associated underlying mechanism have been investigated. Results show that there are two distinct wet periods (1988–2009: Wet Period I; 2010–2021: Wet Period II) of summer rainfall in the Tarim Basin during 1961–2021. The northeast basin has received more summer rainfall during Wet Period I, but during Wet Period II more summer rainfall is concentrated in the west basin, corresponding to different large scale circulation and moisture transport conditions. After the linear trend is removed, the correlation coefficient between the Tarim Basin summer rainfall and the Silk Road pattern index (SRPI) during 2010-2021can reach 0.73, which suggests that the summer rainfall in the west part of the basin is closely related to the Silk Road pattern in this period. In 2010–2021, the meridional wind anomaly center over central Asia in the Silk Road Pattern is located more southward and westward. On the one hand, it causes the location of the anomalous cyclone at 500 hPa over central Asia to stay southward and westward, matching with the anomalous vertical upward motion near 70°E, on the other hand, it also strengthens the anomalous transport of water vapor from the tropical Indian Ocean and Pacific Ocean. The above two provide favorable large scale circulation and abundant water vapor for the increased summer rainfall in the west part of Tarim Basin during 2010–2021.