Extreme Rainfall Events in Asia: Projected Changes and Uncertainties

Monday, June 15, 2015
Nicolas Freychet1, Aurelie Duchez2, Chi-Hua Wu1, Huang-Hsiung Hsu1, Chao An Chen1, Alex Forryan2, Bablu Sinha2, Joel Hirschi2 and Adrian New2, (1)Research Center for Environmental Changes Academia Sinica, Taipei, Taiwan, (2)National Oceanography Centre, Southampton, United Kingdom
Abstract:
Extreme precipitation (and drought) are one of the main concern for society and environment, because they can lead to severe flood (and lack of water supply). In warmer environment, atmospheric moisture is expected to increase, and could thus create more favorable conditions to trigger extreme rainfall. However, the change in dynamics can also play a major role in the change of distribution of precipitation. The modification of the land-sea thermal gradient, the vertical structure of the atmosphere, or the latent heat released by the precipitation, can all impact the large scale circulation, and thus the rainfall distribution.

In this study, focussed on the East Asia region, we analyzed the results from two high resolution models (HiRAM-C192 and HadGEM3-GC2), and from the CMIP5 ensemble, to investigate the projected change in extreme rainfall events (either extreme precipitation or long drought). The role of the SST is also investigate. HadGEM3-GC2 is fully coupled with ORCA025, while HiRAM-C192 is forced by prescribed SST. The SST forcing for this model is determined by a cluster analysis from the CMIP5 projection. Three main patterns of SST are used, providing three different projections for this model. We also emphasize the correlation with the dynamics to explain the internannual variability of the extremes events.

In both CMIP5 ensemble and high resolution models the signal of extreme precipitation strongly increase during the summer. On the other hand, the signal on the drought spell is not clear. HadGEM3-GC2 show a decrease during winter of East Asia, while the three HiRAM runs show an increase during this same season. It could be due to a difference of sea-land contrast. The East Asia 200 hPa Jet intensity impacts significantly the variability of extremes precipitation, while the winter 850hPa winds show a strong correlation with the dought over East Asia. The results on CMIP5 ensemble also show a significant impact of the change in vertical motion (with a tendency to slow down), that could act as a counterbalance to increase of atmospheric moisture. But large uncertainties remain between different models, and impact strongly the confidence on the extreme projection.

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