Scenario Dependence of Future Precipitation Changes across Japan in CMIP6

A bias-corrected downscaled 1-km mesh future climate dataset across Japan called NIES2020, based on five global climate models (GCMs) selected from the Coupled Model Intercomparison Project Phase 6 (CMIP6), has been used for regional impact assessments and adaptation studies under various emission scenarios. However, it is not yet revealed what determines the scenario dependence of the Japanese precipitation changes unscaled with global mean temperature changes. Here, we disentangled the inter-scenario differences in precipitation changes averaged across Japan. In the CMIP6 GCMs, the ensemble mean precipitation increases more in the mid-21^st century under low-emission scenarios than higher-emission scenarios, consistent with NIES2020. In the low-emission scenarios, rapid reductions of anthropogenic aerosol emissions from East Asia enhance the surface downward shortwave radiation around Japan, promoting evaporation and precipitation. Such high precipitation sensitivity per degree of global warming is confirmed regardless of the season. In contrast, the precipitation increase is most suppressed under a high-emission scenario with weak air pollutant mitigation. Therefore, future precipitation changes across Japan are more constrained by aerosol emission changes than global warming levels, especially in the mid-21^st century. This suggests climate response to air pollutant mitigations needs to be considered for implementing impact assessments and adaptation strategies in Japan.