Future changes in Indian summer monsoon characteristics under 1.5 and 2 ℃ specific warming levels

摘要

The rainfall during Indian summer monsoon (ISM) is very important for the population living in the Indian sub-continent. The recent Paris climate agreement determined to keep the global mean temperature rise well below 2 degrees C and pursue efforts to limit it within 1.5 degrees C. This global temperature rise would influence the ISM mechanism over the Indian sub-continent. This study examines the possible changes in the ISM characteristics at 1.5 and 2 degrees C specific warming levels (SWLs) with respect to the historical period. This analysis uses a set of 12 regional climate simulations under Coordinated Regional Climate Downscaling Experiments-South Asia (CORDEX-SA). The land as well as the oceans shows a warming signature due to the effect of anthropogenic forcings with much higher warming over land. The increase of global temperature to 1.5 degrees C (2 degrees C) SWL leads to an earlier onset of ISM over India by 7 (11) days in the model ensemble. The increasing land-sea temperature contrast gradually increases the strength of the Findlater jet (by 0.5-0.9 m/s), which transports more moisture towards land and causes higher rainfall (increase by 2-10%) over India. The study reveals that under a higher SWL of 2 degrees C the mean rainfall is augmented as compared to that under 1.5 degrees C. However, there exists uncertainty in the findings due to inter-model differences especially for the duration of ISM activity and the spatial distribution of rainfall at different SWLs.