Understanding the Diversity of CMIP6 Models in the Projection of Precipitation Over Tibetan Plateau

A reliable projection of precipitation over the Tibetan Plateau (TP) is crucial for climate adaptation activities in this climate-sensitive region, but existing studies show a large spread in magnitude. Based on Coupled Model Intercomparison Project Phase 6 models, we investigate the TP summer precipitation projection and understand the sources of uncertainty. The results show that the TP exhibits a profound wetting trend throughout the 21st century, with precipitation increasing by 0.64 +/- 0.06 mm day-1 during 2050-2099 under the SSP5-8.5 scenario. The moisture budget analysis indicates that the thermodynamical response to global warming determines the precipitation increase. However, both the thermodynamical and dynamical components contribute to the uncertainty of precipitation projection. The inter-model spread of the thermodynamic term arises from divergent global mean warming, which is closely related to model climate sensitivity. The uncertainty of the dynamic component is driven by model-dependent circulation changes induced by different equatorial Pacific warming rates. The precipitation over the Tibetan Plateau (TP) is crucial for local and downstream ecosystems, influencing millions of people. An accurate projection of future precipitation change is a prerequisite for climate change adaptation activities. Current existing studies show a large spread in the future changes of precipitation over the TP, but the reasons remain inconclusive. Here, we unravel the diversity of climate models in the precipitation projection over the TP by quantifying the contributions of the thermodynamical process related to global warming and the dynamical process related to atmospheric circulation change. While the enhancement of precipitation in the multi-model ensemble mean is dominated by the thermodynamical response, both the thermodynamical and dynamical components are found to be responsible for the uncertainty of precipitation projection. The thermodynamical uncertainty is due to divergent global mean warming, which is closely associated with climate sensitivity, implying that models projecting a warmer climate also tend to project a stronger thermodynamical change. The uncertainty of the dynamic component is driven by air circulation changes induced by the equatorial Pacific warming pattern, which further affects the water vapor transport to the TP. Future projection of the Tibetan Plateau (TP) summer precipitation exhibits a large inter-model spread in the magnitude of moistening trend The uncertainty of precipitation projection arises from both the thermodynamical and dynamical process The thermodynamical uncertainty is related to climate sensitivity, while the dynamical spread is driven by the equatorial Pacific warming