India could face extremely wet monsoons, may impact over a billion people, says new climate analysis


Latest climate models project an increase in severity and frequency of wet Indian summer monsoon seasons, a new study by scientists from the Potsdam Institute for Climate Impacts Research (PIK) shows.

The South Asian monsoon affects the lives of more than one billion people and a changing monsoon might have tremendous consequences for millions faced with floods and landslides. The researchers said “very wet monsoon seasons” are projected to occur eight times more often in 2050-2100 compared to 1965-2015 under unabated climate change.

With modest mitigation efforts, this is reduced to a factor of six in the future period. Besides, this increase in frequency and intensity of extreme monsoon seasons is accompanied by a shift from days with light rainfall to days with moderate or heavy rainfall. Additionally, the number of wet days is projected to increase.

This change is directly related to humankind’s determination to reduce carbon emissions and implement mitigation measures. the study said.

There have been numerous floods in recent years associated with the Indian summer monsoon (ISM) as a component of the South Asian monsoon.

The researchers cited as examples the Mumbai flood in July 2005, floods in Northwest India and Pakistan in 2010 as a response to a strong La Nina event or those in Kerala in 2018.

Since the 1980s, there have been more than 95,000 deaths associated with floods and landslides in the countries of the Indian subcontinent.

Given the agricultural yield’s sensitivity to the monsoon rainfall variability and associated extremes, understanding how the ISM responds to global warming is also crucial for crop yields and food security in the region as well as for numerous other aspects of public and individual life, like water management or the country’s economy, climate models suggest.

The data from various phases of Coupled Model Intercomparison projects (CMIPs) has been widely used to examine the projected changes in the global climate as well as its different components such as the ISM. In the last generation of climate models – which were the basis of earlier studies on seasonal extremes – studies identified monsoon rainfall features that were not yet well represented in the CMIP5 models.

“There is a widespread agreement among global climate models that the rainfall during the ISM will increase throughout the 21st century,” the study said. “Using 32 models of the latest climate model generation (CMIP6), Katzenberger et al. (2021) quantified the projected summer monsoon rainfall increase to be between 9.7 per cent and 24.3 per cent by the end of the 21st century depending on the underlying emission scenario.”

The PIK researchers said a 2018 study by Kamizawa and Takahashi using 22 CMIP5 models suggests that the changes in the wettest (driest) and second wettest (driest) seasons between 2007-2031 and 2076-2100 projected that the wet seasonal extremes expand over the Indian subcontinent, “but it has to be noted, that focusing on the maxima is a method highly susceptible to the bias of outliers.”

Research by other climate scientists indicate the same, the study said. A 2015 study found that the years with strong monsoon rainfall are expected to increase in frequency as well as severity by the end of the 21st century but the results still had a very strong inter-model spread. Against this background and given the improvements in CMIP6 compared to CMIP5 as explained before, the results of CMIP6 regarding the seasonal extremes are of particular interest.