Abstract
Abstract. The Indian summer monsoon is an integral part of the global climate system. As its seasonal rainfall plays a crucial role in India's agriculture and shapes many other aspects of life, it affects the livelihood of a fifth of the world's population. It is therefore highly relevant to assess its change under potential future climate change. Global climate models within the Coupled Model Intercomparison Project Phase 5 (CMIP5) indicated a consistent increase in monsoon rainfall and its variability under global warming. Since the range of the results of CMIP5 was still large and the confidence in the models was limited due to partly poor representation of observed rainfall, the updates within the latest generation of climate models in CMIP6 are of interest. Here, we analyze 32 models of the latest CMIP6 exercise with regard to their annual mean monsoon rainfall and its variability. All of these models show a substantial increase in June-to-September (JJAS) mean rainfall under unabated climate change (SSP5-8.5) and most do also for the other three Shared Socioeconomic Pathways analyzed (SSP1-2.6, SSP2-4.5, SSP3-7.0). Moreover, the simulation ensemble indicates a linear dependence of rainfall on global mean temperature with a high agreement between the models independent of the SSP if global warming is the dominant forcing of the monsoon dynamics as it is in the 21st century; the multi-model mean for JJAS projects an increase of 0.33 mm d−1 and 5.3 % per kelvin of global warming. This is significantly higher than in the CMIP5 projections. Most models project that the increase will contribute to the precipitation especially in the Himalaya region and to the northeast of the Bay of Bengal, as well as the west coast of India. Interannual variability is found to be increasing in the higher-warming scenarios by almost all models. The CMIP6 simulations largely confirm the findings from CMIP5 models, but show an increased robustness across models with reduced uncertainties and updated magnitudes towards a stronger increase in monsoon rainfall.
Highlights
As one of the integral components of the global climate system, the Indian monsoon provides water to the densely populated region of South Asia
We investigate the mean Indian summer monsoon rainfall and its interannual variability under four different scenarios using 32 global climate models that participated in CMIP6
We found that there are 16 out of 32 models that are able to capture the monsoon rainfall within twice the standard deviation in the period 1985–2015
Summary
As one of the integral components of the global climate system, the Indian monsoon provides water to the densely populated region of South Asia. About 80 % of the annual precipitation over India occurs during the summer period, supplying water to the crops during the prime agricultural season (Bollasina, 2014). The crop yields (especially rice, which is dominant in the region) are highly sensitive to the monsoon rainfall variability (Prasanna, 2014; DeFries et al, 2016). As agriculture contributes to about 20 % of the gross domestic product (Zaveri et al, 2016), the monsoon’s rainfall has an effect on India’s economy (Gadgil and Gadgil, 2006). Understanding the response of the Indian summer monsoon and its interannual variability to different global warming scenarios is critical
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