Transient response of ENSO-monsoon teleconnection in MRI-CGCM2.2 climate change simulations

This study investigates the impact of anthropogenic climate change on the Indian summer monsoon, and the ENSO-monsoon teleconnection, using the transient climate change simulations of the MRI coupled model (MRI-CGCM2.2). In the present simulations atmospheric greenhouse gas (GHG) concentrations and aerosols are varied to represent observed changes during 1850-2000, and from 2001-2100, at the rate prescribed by the SRES-A2 and B2 scenarios to study the response of the monsoon climate during 2071-2100. All India annual temperature shows warming by 2.35 degrees C (1.64 degrees C), while all-India monsoon rainfall (JJAS) indicates an increase by 9% (6%) in SRES-A2 (B2) scenario relative to the present climate (1971-2000). Increase in the monsoon precipitation is evident over parts of south India, parts of the Bay of Bengal and northwest India. The simulations feature stronger warming over South Asia relative to the Indian Ocean, leading to enhanced land-sea temperature contrast. Enhanced moisture in a warmer scenario, coupled with enhanced monsoon circulation, leads to enhanced moisture transport over the Indian region from both the Bay of Bengal and Arabian Sea leading to increased monsoon precipitation. Decomposition of the moisture transport into divergent and non-divergent components shows that the enhanced monsoon rainfall is mainly due to intensification in the non-divergent component of the moisture transport. While strong and continued increase in monsoon rainfall suggests a change towards wetter mean state, warming of summer (JJA) Nino-3 SSTs suggests a change towards warmer El Nino like mean state in the east Pacific. The variability in the Nino-3 SST shows an increasing trend, as well as fluctuations about the trend. The correlation between the Indian monsoon rainfall and Nino-3 SST decrease particularly after 2050. This weakening of ENSO-monsoon relationship is also seen in the form of change in the impact of ENSO events on the intra-seasonal monsoon rainfall over India.