Projected East-West Contrast of Water Budget in Future Climate over the Tibetan Platea

Thursday, 18 December 2014
Akio Kitoh and Osamu Arakawa, University of Tsukuba, Tsukuba, Japan
High-resolution model is necessary to reasonably simulate regional climate over and around the mountainous regions. Here we use a 20-km-mesh global atmospheric general circulation model to investigate possible future changes in water budget over the Tibetan Plateau (TP). The AMIP experiment for the present-day climate reveals an elevation dependency in precipitation, which matches well to the observations, than that obtained by lower resolution models.

Future AMIP-type experiment is performed using CMIP5 multi-model ensemble mean sea surface temperature changes at the end of the 21st century under the RCP8.5 scenario. In the present climate, an east-west contrast in water budget is noted: over the eastern TP, moisture flux convergence and local evaporation is comparable in summertime precipitation, on the other hand, over the western TP, contribution from local evaporation dominates in water budget. In future climate, annual mean surface air temperature increases 5.0 degree C, about 50% higher than the global mean (3.5 degree C). Over TP, precipitation increases. Contribution from increasing evaporation dominates that from increasing moisture flux convergence into TP. A prominent east-west contrast is found in future surface water budget changes. Over the western TP, surface temperature increases more, increasing rate of precipitation is larger, soil moisture becomes wetter, runoff increases more, and moisture recycling or precipitation efficiency becomes larger than over the eastern TP. This suggests that an east-west contrast in surface climate over TP in the present climate becomes smaller in future climate.