Recycling and transport of evapotranspiration over the Tibetan Plateau: Detected by a water vapour tracer method embedded in regional climate model

With an average elevation of 4000 m, the Tibetan Plateau (TP) exerts a global influence on weather and climate. To investigate and quantify the impact of terrestrial evapotranspiration (ET) over the TP on both local and downstream regions, we employed the water vapour tracer (WVT) method integrated into the Weather Research and Forecasting (WRF) model to track the propagation of evaporative moisture across the TP. Based on precipitation landing location, termination of evaporative moisture over the TP was categorized into recycled ET (ETin, which precipitates inside the TP) and moving-out ET (ETout, which precipitates outside the TP). Our findings reveal that ETin dominates 70% of ET moisture termination over the TP, exhibiting a decrease gradient from eastern to western regions. The majority of ETout spreads eastward with some reaching southward. Seasonal variations indicate that more than 75% of ET recycles during summer, while more ET moves out from TP in spring and autumn. The interplay between convection and advection leads to different reach-outs for moving-out ET in summer compared to other seasons: strong convection and diabatic heating plus a relative weak large-scale advection result in shorter reach-outs during summer, whereas weaker convection combined with strong advection leads to longer -reach-outs in other seasons. This study enhances our understanding of terrestrial ET moisture transport over the TP as well as its mechanism influencing both local water cycle dynamics and downstream processes. The Hovmoller diagram of the ET precipitation during summer (a) and autumn (b) of 2014 reveals a predominant recycling of ET within the TP in summer, while a greater outflow of ET in observed in autumn. This study primarily focuses on elucidating the siginificant seasonal variations and underlying mechanisms governing ET dynamics over the TP. image