Seasonal characteristics of future climate change over Japan and the associated atmospheric circulation anomalies in global model experiments

Information on future climate change considering regional characteristics is necessary to establish adaptation strategies for global warming. We investigated the seasonal characteristics of future climate projections over Japan and surroundings (JPN) in the late 21st century, focusing especially on the source of uncertainty, based on two ensembles of the Coupled Model Intercomparison Project Phase 5 (CMIP5) and the Meteorological Research Institute atmospheric general circulation model (MRI-AGCM) global warming simulations. The ensemble mean surface air temperature increase over JPN is lower than that over the East Asian land region (EAS), reflecting the continent-ocean contrast, whereas quantitative changes in future precipitation depend on the ensembles. The CMIP5 mean atmospheric circulation around JPN weakens in winter and summer, while the future seasonal march tends to be delayed in the northern part of JPN during spring and autumn. Significant CMIP5 inter-model correlations are detected between the JPN climate projections and future circulation anomalies - e.g. the ensemble members simulating the westerly/southeasterly wind anomaly tend to project hotter/wetter future summers. The high-resolution MRI-AGCM projection is consistent with the CMIP5 inter-model correlations when the future change in typhoon-associated precipitation is removed, indicating typhoon simulations can substantially influence future projections.