Projected changes in mean temperature, precipitation and extreme snowfall events over the Tibetan Plateau based on a set of RegCM4 simulations

Tibetan Plateau (TP, with the height > 3000 m) is a region with complex topographical features and a large diversity of climate both in space and time. Future climate change over TP and the surrounding areas is investigated based on the ensemble of a set of the 21st century climate change projections using a regional climate model, RegCM4. The model is driven by five different GCMs at a grid spacing of 25 km. Results show the RegCM4 greatly improves the temperature and precipitation simulations by providing finer scale spatial details of them over the region. The topographic effects are well reproduced by RegCM4 but not the GCMs. General warming and increase in precipitation are found in both GCM and RegCM4 simulation, but with substantial differences in both the spatial distribution and magnitude of the changes. For temperature, RegCM4 projected a more pronounced warming in DJF over TP compared to its surrounding areas. The increase of precipitation is more pronounced and over the basins in DJF for RegCM4. For the extreme indices of snowfall, RegCM4 generally reproduces the spatial distributions although with overestimation in the amount. General decreases in SNOWTOT and S1mm, with greater magnitude over the eastern part are projected. Both S10mm and Sx5day show decrease over the eastern part but increase over the central and western parts. Notably, S10mm shows a marked increase (more than double) with high cross-simulation agreement over the central TP. Significant increases in all four indices are found over the Tarim and Qaidam basins, and northwestern China north of the TP. The projected changes show topographic dependence over the TP in the latitudinal direction, and tend to decrease/increase in low-/high-altitude areas.