Effects of Soil Moisture in Northern Tibetan Plateau on Summer Precipitation in Northwest China

Abstract

Soil moisture (SM) on the Tibetan Plateau (TP), a crucial climate variable with “memory,” influences the East Asia climate by modulating surface energy and water vapor exchanges. Understanding the relationship between TP soil moisture (TPSM) and summer precipitation in Northwest China (NWC) is essential for improving climate predictions for East Asia. However, most existing studies have focused on the connection between TPSM and the climate of East Asian monsoon region, whereas the mechanisms by which TPSM influence precipitation in NWC, a nonmonsoonal area, remain underexplored. This study investigates how spring anomalies of TPSM persist into summer and influence summer precipitation in NWC. The results indicate that anomalies in spring TPSM can initiate a positive feedback with precipitation, which affects the intensity of plateau monsoon and contributes to the persistence of SM anomaly from spring to summer. During summer, positive SM anomalies in northern TP facilitate maintaining cyclonic circulation anomalies over western TP and trigger eastward-propagating Rossby waves that induce anticyclonic circulation anomalies over eastern NWC. The anomalous circulation results in upward motion in the western NWC and subsidence in the eastern NWC enhancing precipitation in the western NWC while reducing the precipitation in the north. Finally, the findings from the circulation analysis are validated through numerical model simulations. This study provides valuable insights into the climatic effects of TPSM and offers important implications for precipitation prediction in NWC.