Summer heat sources changes over the Tibetan Plateau in CMIP6 models

Abstract

The elevated summer heat sources over the Tibetan Plateau (TP) profoundly influence Asian monsoon and atmospheric general circulation. Model simulations and future changes of condensational latent heat released from precipitation and surface sensible heat (SH) over the eastern TP are investigated with 22 CMIP6 models’ outputs. The models reproduce the mean precipitation pattern well, but the mean intensity is 65% excessive. The SH has scarcely been evaluated. We find that nearly half of the models cannot realistically capture the SH’s spatial structure. The best six models in simulating the SH are the same models that best simulate surface air temperature. The models with high performance are selected to make a multi-model ensemble mean projection. Under the medium emission scenario (SSP2-4.5), the TP’s future summer precipitation will likely increase, despite its weakening thermal forcing effect. The increasing precipitation is primarily due to the future enhancement in vertical moisture transport and surface evaporation. However, the greenhouse gases-induced top-heavy heating stabilizes the atmosphere and diminishes the TP’s thermal forcing effect, weakening the circulation and upward motion. As such, the precipitation sensitivity is only a 2.7% increase per degree Celsius global warming. The projected SH will be likely unchanged in accord with the likely unaltered surface wind speed. These results have important implications for the future change of the water supplies in the heavily populated South and East Asian countries. They could help the modeling groups further improve the climate model performance in the highland regions.