Contribution of Recycled and External Advected Moisture to Precipitation and Its Inter-Annual Variation Over the Tibetan Plateau

In this study, we performed a high-resolution simulation using the Weather Research and Forecasting model, integrated with water vapor tracers, covering the years 2005-2019. Our objective was to obtain deeper insights into the spatiotemporal dynamics of external advected and local evaporative water vapor, and to elucidate their impact on precipitation patterns across the Tibetan Plateau (TP). Our findings underscore that a significant proportion of TP's precipitation originates from external advected water vapor, primarily entering through the western and southern boundaries. During summer, stronger zonal and meridional water vapor transport, driven by prevailing westerly winds and the Asian monsoon, significantly influences seasonal and spatial precipitation variations. Additionally, we observed that the inter-annual variation of precipitation is intricately linked to changes in the net water vapor influx, modulated by alterations in atmospheric circulation. We also analyze the Precipitation Recycling Ratio (PRR) which refers to the proportion of precipitation originated from local evaporative water vapor to the total precipitation, revealing distinctive elevation-dependent variations aligned with grassland distribution. Notably, PRR exhibits asynchronous shifts with precipitation at different timescales, potentially linked to soil moisture-precipitation feedback at intra-annual scales. Moreover, the investigation highlights that inter-annual variations in PRR are primarily linked to the inflow and outflow of water vapor as well as wind strength at 500 hPa, particularly prominent during colder seasons, while thermal factors carry comparable weight to dynamical factors in warmer seasons. Precipitation constitutes a vital component of the complex climatic conditions as well as the hydrological cycle over the Tibetan Plateau (TP), known as the "Asian Water Tower." Its distinct spatiotemporal variations, closely tied to the advected water vapor from external areas as well as evaporated within the TP, have direct impacts on local ecosystem and downstream water supply. These effects have profound socio-economic and environmental consequences. In this study, we found that temporal variations and spatial inhomogeneities in precipitation are primarily impacted by the advection of external water vapor, mainly through atmospheric circulation. Additionally, about 18.9% of the annual precipitation stems from local evaporation, as indicated by the precipitation recycling ratio, which reflects the strength of regional land-atmospheric interactions. Precipitation recycling processes are likely influenced by precipitation through soil moisture at intra-annual timescale, but are notably impacted by the inflow of water vapor and wind strength at inter-annual timescale. These results provide valuable insights into understanding precipitation variations at different spatiotemporal scales and contribute to more effective water resources management over the TP. Precipitation recycling ratio (PRR) over the Tibetan Plateau exhibits significant variations both with elevation and from year to year The inter-annual variation of precipitation is strongly influenced by the net influx of water vapor and associated atmospheric circulations Inter-annual variation in PRR is significantly influenced by the inflow of water vapor and wind strength, especially during colder seasons