Diagnosis of ENSO-related precipitation changes during the twentieth and twenty-first centuries using reanalyses and two multi-model clusters

Abstract

Changes in El Nino-Southern Oscillation (ENSO)-related precipitation anomalies during the twentieth century are poorly known. The ENSO-related precipitation anomalies over the tropical Pacific Ocean are projected to shift eastward during the twenty-first century. However, intermodel diversity in simulating and projecting these changes has not been fully studied. Understanding such diversity is vital for providing robust projections of future changes in the ENSO-related precipitation. Here, we use an approach that can cleanly separate ENSO signals from long-term variations to study multi-decadal and centennial changes of ENSO-related precipitation anomalies during the twentieth and twenty-first centuries in two precipitation reanalyses and two groups of the Coupled Model Intercomparison Project Phase 5 (CMIP5) models. The two precipitation reanalyses disagree in the multi-decadal changes during the twentieth century: precipitation anomalies in the twentieth century global circulation reanalysis indicates zonal shifts of the positive and negative ENSO-related precipitation anomalies, whereas reconstructed precipitation derived from observations suggests an intensification of the anomalies. Most members of the ensemble of 20 CMIP5 models project significant strengthening or zonal shift in ENSO-related precipitation during the twenty-first century, which is almost entirely influenced by changes in the ENSO-related circulation from a moisture budget analysis. The ‘good-ENSO’ group with stronger ENSO atmospheric feedbacks projects an intensification of ENSO-related precipitation anomalies over the eastern-central equatorial Pacific, as a result of strengthened deep convection anomalies in the middle to upper troposphere above. This increased variability of convection is driven by a warmer SST mean state of the central-eastern Pacific Ocean. The underperforming group that simulates colder equatorial SSTs, weaker atmospheric feedbacks, and more westward extended ENSO-related precipitation anomalies, exhibits both strong intensification and eastward shift of the entire ENSO-related air–sea interactive system and the related precipitation over the western-central Pacific during the twenty-first century, in correspondence with a mean-state SST warming in the entire equatorial Pacific. Our clustered results suggest that the changes of ENSO-related precipitation are closely tied with the historical simulation of structure of the ENSO-related air–sea system and the projection of changes in the mean-state SST under global warming.