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El Nino-Southern Oscillation (ENSO) plays a dominant role in interannual climate variability in Pacific island countries, directly affecting lives there. Many countries show different rainfall responses depending on the sea surface temperature (SST) structure of different types of El Nino events. El Nino events are classified into three types based on previous studies: those with strongest SST anomalies in the eastern Pacific Cold Tongue region (CTE), in the Western Pacific Warm Pool region (WPE), and those in between, a “Mixed” El Nino (MxE), and results from 30 CMIP5 models are investigated. These models accurately reproduce observed SST and precipitation anomalies for the three El Nino types and La Nina. CMIP5 models simulate much larger ranges in the strength of ENSO events than observed. Results clarify the roles of both the different structures of El Nino SST anomalies and their magnitudes on rainfall in the Pacific, and demonstrate that each of the three El Nino types has different impacts on rainfall in the region. These impacts vary with location, with WPE and CTE producing very different impacts in most Pacific island countries. There is a linear intensification of both the mean and maximum rainfall anomalies in the equatorial Pacific as the events become stronger. Equatorial rainfall shifts eastward in CTE and MxE, westward in La Nina. Both the South Pacific and Intertropical Convergence Zones (SPCZ and ITCZ) shift equatorward in El Nino and poleward in La Nina, the shifts increasing as events strengthen. WPE show different behaviour to other events, with little east-west shift in equatorial rainfall, and the orientation angle of the convergence zones increases. Identification of models with no erroneous westward bias in SST anomalies has clarified the effect of strong CTE events producing “zonal” SPCZ and shifting rainfall away to the east from western equatorial countries.

Intermittent disruptions to rainfall patterns and intensity over the Pacific Ocean lasting up to ∼ 1 year have major impacts on severe weather, agricultural production, ecosystems, and disease within the Pacific, and in many countries beyond. The frequency with which major disruptions to Pacific rainfall occur has been projected to increase over the 21st century, in response to global warming caused by large 21st century greenhouse gas emissions. Here we use the latest generation of climate models to show that humans may have contributed to the major disruption that occurred in the real world during the late 20th century. We demonstrate that although marked and sustained reductions in 21st century anthropogenic greenhouse gas emissions can greatly moderate the likelihood of major disruption, elevated risk of occurrence appears locked in now, and for at least the remainder of the 21st century., Intermittent rainfall changes over the Pacific Ocean can profoundly disrupt lives and ecosystems in many locations. Here, the authors show that the risk of such changes has increased, and that the risk could – even with a reduction in greenhouse gas emissions - remain elevated for decades to come.