Future impacts of two types of El Nino on East Asian rainfall based on CMIP5 model projections

In this study, future change of El Nino-related East Asian (EA) rainfall and the diversity of this relationship are investigated on the basis of the historical and representative concentration pathway 8.5 (RCP 8.5) simulations taken from the Coupled Model Intercomparison Project phase 5 (CMIP5). By evaluating the East Asian Summer Monsoon (EASM) climatology and interannual variations in simulations contributing to CMIP5, nine models are verified to be capable of reproducing El Nino diversity and EASM simultaneously. Six of these models are selected for projecting the multi-model ensemble (MME) mean of two types of El Nino-related EA/western North Pacific (WNP) rainfall patterns and low-level atmospheric circulations under global warming, considering the realism in their simulated El Nino and EASM phenomena. It was found that, under a warmer background climate, the general patterns of anomalous circulation and rainfall will persist, but with amplification of the rainfall intensity during mature boreal winter and decaying summer for both Eastern-Pacific (EP) and Central-Pacific (CP) El Nino. Amplification of CP type-related rainfall seems to be stronger than that for EP type El Nino. Further analyses show that a moister atmosphere tends to always strengthen the rainfall variations for both El Nino flavors, regardless of how the El Nino-related circulation amplitude is modulated in various seasons. However, in boreal summer during the El Nino decaying phase, strengthened anomalous circulation also enhances the rainfall variability, with an effect comparable to the background moisture increase. Some of these atmospheric circulation changes might be associated with modified sea surface temperature anomalies (SSTA) of El Nino and its diversity, under global warming. Our results indicate the importance of better preparedness and higher resilience in the EA region to enhanced El Nino-induced hydrological variations under a warming climate.