Evaluation of the Global Climate Models in the CMIP5 over the Tibetan Plateau

The performance of 24 GCMs available in the fifth phase of the Coupled Model Intercomparison Project (CMIP5) is evaluated over the eastern Tibetan Plateau (TP) by comparing the model outputs with ground observations for the period 1961-2005. The twenty-first century trends of precipitation and temperature based on the GCMs' projections over the TP are also analyzed. The results suggest that for temperature most GCMs reasonably capture the climatological patterns and spatial variations of the observed climate. However, the majority of the models have cold biases, with a mean underestimation of 1.1 degrees-2.5 degrees C for the months December-May, and less than 1 degrees C for June-October. For precipitation, the simulations of all models overestimate the observations in climatological annual means by 62.0%-183.0%, and only half of the 24 GCMs are able to reproduce the observed seasonal pattern, which demonstrates a critical need to improve precipitation-related processes in these models. All models produce a warming trend in the twenty-first century under the Representative Concentration Pathway 8.5 (rcp8.5) scenario; in contrast, the rcp2.6 scenario predicts a lower average warming rate for the near term, and a small cooling trend in the long-term period with the decreasing radiative forcing. In the near term, the projected precipitation change is about 3.2% higher than the 1961-2005 annual mean, whereas in the long term the precipitation is projected to increase 6.0% under rcp2.6 and 12.0% under the rcp8.5 scenario. Relative to the 1961-2005 mean, the annual temperature is projected to increase by 1.2 degrees-1.3 degrees C in the short term; the warmings under the rcp2.6 and rcp8.5 scenarios are 1.8 degrees and 4.1 degrees C, respectively, for the long term.