Climate Change Is Making The Monsoon More Dangerous

In the early hours of June 28th your correspondent was woken by an almighty crash of thunder. The other side of the street had vanished behind a wall of water: the monsoon had arrived in Delhi.

By the end of the day, 23cm of rain had fallen on India’s capital, three times more than it usually gets in the entire month of June, making it the rainiest 24 hours since 1966.

The forecourt roof of a recently refurbished airport terminal collapsed, killing a taxi driver. Ten more people died in “rain-related incidents”.

People in parts of India and South Asia can probably expect more days like this. Since the middle of the 20th century the number of “extreme rain days” (defined as more than 150mm of precipitation in 24 hours) in India has gone up. Global warming appears to be making the monsoon more variable. And as temperatures rise further, the monsoon’s extremes could become more damaging.

In an ideal year the monsoon brings plentiful (but moderate) rain to India between June and September, irrigating crops and replenishing groundwater as it moves steadily northward from the country’s southern tip. Of course, things are often different in reality. The monsoon is influenced by a huge range of factors, and has always been a notoriously tricky weather system to forecast. It often turns up in fits and starts. Long dry spells are followed by sudden deluges, which parched earth or city sewerage can struggle to absorb. But as the climate heats up, these variations seem to be growing more pronounced (see chart).

A warmer atmosphere can hold more moisture; warmer oceans mean more water evaporates up into it. The Indian subcontinent should expect 5.3% more precipitation during the monsoon for every additional degree Celsius of global temperature rise, according to a study published in 2021. And this extra rain looks more likely to be dumped all at once than spread evenly. “You frequently get droughts and floods in the same place in the same season now,” says Roxy Mathew Koll, a climate scientist at the Indian Institute of Tropical Meteorology in Pune, a city in Maharashtra.

The places that tend to get the most and least rain are changing, too. Some of north-central India’s agricultural regions are getting drier, even as other parts of the country grow drenched.

Unpredictability is bad news for India’s farms, 60% of which have no access to water other than from the sky. Trends in the monsoon affect when farmers choose to sow and harvest their crops; this year, for example, a limp start to the monsoon delayed sowing season in some places. Over the past decade, forecasters have been getting better at predicting the monsoon’s national and regional patterns, says Yogesh Patil of Skymet, a forecasting company in Mumbai. Yet forecasts at the local level still founder. Nobody foresaw the scale of the deluge in Delhi, or a more recent massive downpour in Mumbai.

Mr Patil hopes better data will help. His company draws information from 5,500 sensors around the country; the government maintains another 1,500. The agriculture ministry is now championing a plan to make land available for companies, such as Skymet, to set up tens of thousands more. The northern state of Uttar Pradesh, for example, could end up hosting some 50,000 rain sensors. Other states may follow suit. “Once they have collected data for three years or so, our local models should improve a lot,” reckons Mr Patil. He also hopes for better co-operation between different government bureaucracies, such as the agriculture ministry and the disaster-management authorities.

Yet forecasting can do only so much. Adaptation will also be essential if South Asian countries are to limit the death and destruction the rains cause each year. Farms need better irrigation systems, both to water thirsty crops and to weather harsh storms. Building more reservoirs, or reactivating old ones, would help store water from excessive rainfall, rather than letting it go to waste. Cities and villages need better drainage, too. In recent years Indian cities have begun developing “heat action plans”, designed to help their inhabitants cope with more frequent heat waves. But Mr Koll thinks there is not nearly as much thought going into dealing with floods. It would be a bad idea to wait until the next monsoon before getting those afloat.