On the Projected Decline in Droughts Over South Asia in CMIP6 Multimodel Ensemble

Recent studies based on the ensemble mean of Coupled Model Intercomparison Project 6 (CMIP6) General Circulation Models (GCMs, CMIP6-GCMs hereafter) reported a decline in drought frequency over South Asia in the projected future climate. Here using the simulations from 16 CMIP6-GCMs, we examine the potential causes of declining droughts in South Asia. We show that the projections based on the multimodel ensemble mean CMIP6-GCMs are not reliable over South Asia. The multimodel ensemble mean is influenced mainly by the low-skill GCMs, which show high bias in simulating the monsoon (June-September) season precipitation during the observed period (1951-2014). The low-skill GCMs show a higher (20-30%) increase in the convective precipitation with a rise in the global mean temperature under the warming (1.5 degrees C, 2.0 degrees C, and 2.5 degrees C worlds) climate. The GCMs with less bias (BEST-GCMs) in the monsoon season precipitation and better seasonal cycle representation show lower sensitivity of convective precipitation to rise in global mean temperature. BEST-GCMs exhibit significantly different projections in comparison to the multimodel ensemble mean from all 16 GCMs (ALL-GCMs). In contrast to ALL-GCMs, BEST-GCMs project an increase in the frequency of droughts in South Asia under the future climate. Therefore, the projected risk of droughts over South Asia under the 1.5 degrees C, 2.0 degrees C, and 2.5 degrees C warming levels is higher than previously reported based on the ensemble mean of CMIP6-GCMs. A projected increase in the drought frequency in South Asia will have considerable implications for agricultural production and water availability.