Climate change will make monsoon storms in South Asia wetter and weaker, with more storms pushing further inland across India.
Scientists from the University of Reading used 13 climate models to understand how warming temperatures will affect monsoon low-pressure systems. These storms deliver more than half of all monsoon rainfall and nearly all extreme rainfall events across South Asia.
The research, published in the Journal of Climate , found that storms will become about 10% weaker by the time global temperatures rise 3°C above pre-industrial levels. Despite becoming weaker, each storm will produce more rain – up to 28% more for the strongest storms. By the time temperatures reach 2°C of warming, average rainfall from each storm will increase by roughly 10%.
Dr Kieran Hunt from the University of Reading and lead author, said: "How can weaker storms produce more rain? It sounds wrong, but the answer partly lies in changes to moisture patterns. Warming temperatures increase the difference in moisture levels between northern and southern India. Winds ahead of storms push this extra moisture into the rainfall zone, making storms wetter even though their winds are slower."
More storms and more flooding
The study suggests the number of monsoon storms will increase as temperatures rise. Models show roughly 15% more storms when temperatures reach 2°C above pre-industrial levels, though the increase varies between 10% and 36% depending on specific atmospheric patterns. The findings also indicate the time storms spend over land after moving from the ocean will increase significantly between 1.5°C and 2°C of warming, meaning western parts of India will face growing flood risks as temperatures rise.
Four possible future scenarios based on different patterns of atmospheric circulation and moisture were created by the researchers, with all scenarios agreeing that more storms will also likely affect regions including Sri Lanka and Bangladesh.
Professor Andy Turner, co-author, said: "We found four different pathways the monsoon could take as the world warms, but the message is the same across all of them. Wetter, more frequent storms will reach areas that rarely see them today. One scenario showed storms could increase by 36% if wind patterns change to bring more disturbances from Southeast Asia into the Bay of Bengal. Whichever path we follow, western India needs to prepare for more flooding."
