Changes in the ENSO–ISMR relationship in the historical and future projection periods based on coupled models

Abstract

AbstractWe examine the projected changes in Indian summer monsoon rainfall (ISMR) and El Niño Southern Oscillation (ENSO) along with their changing relationships by the end of 21st century using Coupled Model Inter Comparison Project Phase5 (CMIP5) models. The historical (1951–2005) and future (2050–2099) projections of ISMR were assessed in addition to the changes in the ENSO–ISMR relationship during both the periods. The future period was selected as 2050–2099 in order to understand how the increase in greenhouse gas emissions and global warming by the end of 21st century will affect the ocean atmosphere interactions over the tropical Pacific Ocean and the associated rainfall characteristics over the Indian region. For the future projection, we considered Representative Concentration Pathways (RCP) 4.5 and 8.5 scenarios for the five models (CNRM‐CM5, GISS‐E2‐R, GISS‐E2‐R‐CC, HadGEM2‐CC and IPSL‐CM5A‐MR), which were selected from the 25 CMIP5 models based on their ability to capture the seasonal cycle and variability in the historical period. Although, all the five models simulate an increase in ISMR in both the RCPs, the increase is well simulated by CNRM‐CM5, HadGEM2‐CC and IPSL‐CM5A‐MR models mainly over the northeast, west coast, foothills of Himalayas, central India and the peninsular Indian regions. Substantial differences in simulating the ENSO–ISMR relationship are observed among the models in both historical and future RCP scenarios, and the observed relationship is well represented in GISS‐E2‐R‐CC, HadGEM2‐CC and IPSL‐CM5A‐MR models. The rainfall over most of the Indian regions shows a significant decrease (increase) during El Niño (La Niña) events in RCP 4.5. The changes in sea surface temperature (SST) anomalies and Walker circulations over the Indo‐Pacific region during El Niño and La Niña events are connected with the ISMR characteristics during these events in the RCP 4.5 scenario. On the other hand, the Indo‐Pacific region undergoes total warming (cooling) during El Niño (La Niña) events, and the Indo‐Pacific SST does not exhibit significant variability in the RCP 8.5 scenario. Hence, they are not well related with the observed ISMR patterns in that scenario.