Projected Changes in Precipitation Recycling over the Tibetan Plateau Based on a Global and Regional Climate Model

摘要

Precipitation recycling, as represented by the precipitation contributed by locally evaporated water vapor, is a key indicator of regional changes in the water cycle. The quasi-isentropic back-trajectory method, combined with a global climate model Community Climate System Model (CCSM) and regional climate model Weather Research and Forecasting (WRF) Model simulation forced by CCSM (WRF-CCSM), was used to analyze historical (1982-2005) and future (2090-99) precipitation recycling over the Tibetan Plateau (TP). The study focuses on the differences in the projection of precipitation recycling ratio (PRR) changes and relevant mechanisms between the fine-resolution (30 km) WRF-CCSM and coarse-resolution (similar to 110 km) CCSM simulations. Compared with CCSM, the biases and root-mean-square errors of the historical evapotranspiration and precipitation over the TP were greatly reduced in the WRF-CCSM simulation, particularly in precipitation. UsingWRF-CCSMoutputs, higher PRRs in all elevation bands than CCSM, as well as the opposite seasonal pattern and linear trend of PRR for the river basins in the northern TP, were revealed. Unlike the CCSM projections, WRF-CCSM projects increasing trends of PRR changes with elevation under the RCP4.5 and RCP8.5 scenarios, with the largest increase at an elevation of about 5000 m. WRF-CCSM projects a diverse spatial and seasonal pattern of PRR changes, in contrast to the uniform decrease projected by CCSM. The larger fractional increases of future evapotranspiration contribution (precipitation contributed by local evapotranspiration) per unit warming than precipitation changes in WRF-CCSM suggests an enhanced contribution of locally evaporated moisture to total precipitation in the future under the RCP4.5 and RCP8.5 scenarios.