Robust increase of Indian monsoon rainfall and its variability under future warming in CMIP-6 models

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 (CMIP-5) indicated a consistent increase in monsoon rainfall and its variability under global warming. Since the range of the results of CMIP-5 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 CMIP-6 are of interest. Here, we analyse 32 models of the latest CMIP-6 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 high agreement between the models and independent of the SSP; the multi-model mean for JJAS projects an increase of 0.33 mm/day and 5.3 % per degree of global warming. This is significantly higher than in the CMIP-5 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 CMIP-6 simulations largely confirm the findings from CMIP-5 models, but show an increased robustness across models with reduced uncertainties and updated magnitudes towards a stronger increase in monsoon rainfall.

Model Uncertainty in the Projected Indian Summer Monsoon Precipitation Change under Low-Emission Scenarios

“…The present study also highlights that ISM precipitation change displays large differences between CMIP5 and CMIP6 models, which is also confirmed by results under high-emission scenarios [50]. The reasons causing the distinct ISM response between CMIP5 and CMIP6 models, especially the interhemispheric warming contrast, is worthy of further in-depth study.…”

“…Following an increased NH-SH warming gradient in CMIP6 compared to CMIP5 (blue and red stars in Figure 11d), the ISM precipitation also increases significantly. This suggests that the distinct ISM circulation and precipitation change between CMIP5 and CMIP6 can be largely explained by the differences in interhemispheric warming contrast, which may be further related to the enhanced Arctic warming (Figure 10b), substantially different cloud simulation, deep convective schemes in CMIP6 compared to CMIP5 [46][47]50]. Indeed, the CMIP6 models is revealed to be more capable than CMIP5 models in reproducing the spatial and temporal pattern of ISM [16], this may also contribute to some extent.…”

Climate change projections over Indus basin using CMIP6 model simulations

“…Studies revealed that the precipitation obtained from the CMIP6 models show a continuous increase compared to that of in CMIP5 models over different parts of the world, South Asian countries, particularly Zhu et al, (2020); Almazroui et al, (2020). Studies also show that CMIP6 has better skills in representing the rainfall than CMIP5 over Asia's regions (Chen et al, 2021), India (Katzenberger et al, 2021). Therefore, it is evident that the increase in precipitation is observed in both seasons under different emission scenarios (SSP2-4.5 & SSP5-8.5).…”

Extreme weather impacts of climate change: an attribution perspective

“…Annual monsoons are a critical source of rainfall for at least 60% of the world's population in areas including south and east Asia, Australia, and east and west Africa (Li et al 2016). The south Asian monsoon is of particular societal importance, providing 80% of the water to the subcontinent, which contains nearly a fifth of the world's population and is heavily reliant upon agriculture (Katzenberger et al 2021). In the 20th Century, a decline in the East Asian summer monsoon rains was observed, with the most intense rains becoming shorter but more intense, including flooding and droughts (Burke and Stott 2017).…”

“…In the 20th Century, a decline in the East Asian summer monsoon rains was observed, with the most intense rains becoming shorter but more intense, including flooding and droughts (Burke and Stott 2017). Since 2000, the strength of south Asian monsoon rains has increased, with the most pronounced increases occurring in the most intense events (Katzenberger et al 2021). This pattern covers all monsoon regions, to varying degrees, and crucially an associated increase in both drought and flooding Stott 2017, Wang et al 2021).…”