Future climate simulations generally suggest an increase in monsoon rainfall on a seasonal mean, area-average basis. This is due to the twin drivers of an increasing land-sea thermal contrast, but more importantly, warming over the Indian Ocean, allowing more moisture to be carried to India. Typically increases in total rainfall over India may be in the region of 5-10%, although some climate models suggest more and some less. Climate simulations also show different patterns of rainfall change, so it is difficult to predict how rainfall might change within India.

A 5-10% change in total rainfall sounds small – does it matter to life in India? The Indian monsoon is remarkably stable as a whole, with a mean total of around 850mm from June to September and an interannual (year-to-year) variation of only around 10% in most cases. However, even these relatively small variations in the Indian monsoon can influence things like agricultural production and the stocks and commodities market, so a 5-10% change on top could have significant impacts.

For many people in India, the variability of rainfall on shorter time scales has the most significant impacts – intense heavy rainfall leads to flooding; breaks in the monsoon of a week or more lead to water shortage and agricultural drought.

Floods and droughts are a regular occurrence in India. In 2002, for example, a break in the monsoon rains saw July receiving only about 50% of its normal rainfall, leading to cuts in agricultural output and declining GDP. Thinking about climate change in how these extreme events will change can help farmers and other end users understand its implications.