Inter-Model Differences of Future Precipitation Changes in CMIP3 and MIROC5 Climate Models

The projected changes in annual mean precipitation and large-scale circulations between the two periods 1981-2000 and 2081-2100 obtained from the Coupled Model Intercomparison Project phase 3 (CMIP3) and version 5 of the Model for Interdisciplinary Research on Climate (MIROC5), which is a newly developed model and not included in CMIP3, are investigated over tropical oceans (30 degrees S-30 degrees N). We first evaluate skill scores for precipitation reproducibility, based on which five highest and lowest score models (HSMs and LSMs) are selected from 24 CMIP3 models. The score of MIROC5 is higher than that of any CMIP3 model without flux adjustment. While the HSMs, the LSMs, and MIROC5 commonly show precipitation increase over the equatorial central to eastern Pacific region, and weakening of the Walker circulation in future projections; the magnitudes of these changes are significantly larger in the HSMs than in the LSMs. This difference in the magnitudes of the changes between in HSMs and in LSMs is consistent with the different sensitivities of deep convection to the environmental humidity in the mid-lower troposphere. The vertical structure of the vertical velocity changes indicates that the precipitation increase around 160 degrees E-150 degrees W in the HSMs and LSMs is associated with deep convection, whereas that in MIROC5 is associated with middle-level convection.