Variations of water vapor transport and water vapor-hydrometeor-precipitation conversions during a heavy rainfall event in the Three-River-Headwater region of the Tibetan Plateau

Abstract

A summertime torrential heavy rainfall event which was occurred in the eastern Three-River-Headwater region (TRHR) of the Tibet Plateau (TP) was simulated by the Weather Research and Forecasting (WRF) model. Variations of three-dimensional water vapor transport and water vapor-hydrometeor-precipitation conversions were analyzed in complex terrains. The results show that: before and in the beginning of the precipitation, the surface evaporation (ES) in the forenoon is the most important water vapor source of hydrometeor formation (Micss), and is much larger than water vapor flux convergence (Qvac). During the developmental stage in the afternoon, Qvac surpasses ES, and contributes the most hydrometeor mainly through condensation (Qcon) for the sporadic precipitation on the mountains, which is related to the convergence of the vertically integrated water vapor flux (IWVF) belts from the northern lower altitude under the topography-forced and thermal-driven uplift with the southerly water vapor flux. During the mature stage at night, the northerly and southerly water vapor fluxes merge and transport eastward downhill, converge further with another easterly stronger IWVF belt, leading to the local heavy rainfall on the lower topography slope. The hydrometeor generated by Qcon and deposition (Qdep) is the primary source of heavy precipitation, while the weak precipitation is prone to directly come from the hydrometeor convergence (Qhc) and local hydrometeor consumption (Qhl). During the dissipative stage before the dawn, the persistence of precipitation is significantly through the consumption of local accumulated water vapor (Qvl) and hydrometeor (Qhl). This study is helpful to provide scientific reference for the rational development and utilization of local cloud water resources and the local disastrous weather prevention and reduction.