Future projection of Indian summer monsoon variability under a high emission climate change scenario using CMIP5 climate models

This study investigates the impact of enhanced anthropogenic greenhouse gas emissions on the possible future changes in different aspects of the Indian summer monsoon (ISM) variability using 20 Coupled Model Intercomparison Project Phase 5 (CMIP5) climate models. The historical (1951-1999) and future (2051-2099) simulations under the highest emission Representative Concentration Pathway scenario (RCP 8.5) have been analyzed. A few reliable models are selected based on their competence in simulating the basic features of present-climate ISM variability. Robust and consistent projections across the selected models suggest substantial changes in the ISM variability by the end of 21st century, indicating strong sensitivity of the ISM to global warming. On the seasonal scale, the all-India summer monsoon mean rainfall is likely to increase moderately in future, primarily governed by enhanced thermodynamic conditions due to atmospheric warming, but slightly offset by weakened large scale monsoon circulation. On interannual timescales, it is speculated that the severity and frequency of both strong monsoon (SM) and weak monsoon (WM) conditions might increase noticeably in the projected future climate. Substantial changes in the daily variability of ISM are also projected, largely associated with the increase in heavy rainfall events and decrease in both low rain-rate events and the number of wet days during the future monsoon. On the subseasonal scale, the model projections depict considerable amplification of higher frequency (less than 30-day period) components, although the dominant northward propagating 30-70 day mode of monsoon intraseasonal oscillations may not change appreciably in a warmer climate. It is speculated that the enhanced high frequency mode of monsoon ISOs due to increased greenhouse gas-induced warming may notably modulate the ISM rainfall in a future climate. Both extreme wet and dry episodes are likely to intensify and regionally extend in the projected future climate. In addition, the SM (WM) could also be more wet (dry) in future, due to the increment in longer active (break) spells. Nevertheless, future changes in spatial patterns of rainfall during the active/break phases of SM and WM are geographically inconsistent among the models. The results point out the growing climate-related vulnerability of the Indian subcontinent.