Climate change is remaking the monsoon in South Asia

SFROM ARRIVAL Two days late at its usual landing point at Thiruvananthapuram in Kerala, near the southern tip of India, South Asia’s annual summer monsoon has made up for lost time. Ripping through the north, rainy southwest winds covered four-fifths of the country in the first two weeks of June, reaching even the most northeastern states of India. The western arm of the monsoon has yet to reach the states of Gujarat, Haryana and Rajasthan. But Yogesh Patil, director of Skymet, a private weather forecasting service, predicts the monsoon will cover the entire country by July 8, around its average date.

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Bangladesh, Bhutan, Nepal and Pakistan are also beneficiaries of the South Asian monsoon. It affects more than 1.8 billion people, or nearly a quarter of the world’s population. Although its circulation is complex, at its heart the summer monsoon is a sea breeze that operates on a continental scale throughout the season. A rapidly warming Indian subcontinent is pushing hot air up above. This attracts the wetter maritime air from the Indian Ocean. As this air rises, it cools and falls as rain. The northern Himalayan wall amplifies the effect.

The arrival of the monsoon is a cause for celebration. Over 70% of annual precipitation falls in just four months. It refreshes the fierce summer heat and waters a thirsty land. The Ganges and other rivers fill and spread a rich silt over the flood plains. The sown crops have finally grown. Agriculture provides almost half of all jobs in India and accounts for almost 20% of GDP (most farmers depend on rainfed crops rather than irrigation). A bad monsoon can reduce economic growth by a third, drive farmers into scarcity and create ripple effects on government revenues when they are needed most. The remark of a British imperial administrator that the Indian budget is “a gamble in the rain” remains true today.

However, the monsoon is not a uniform wave. It is crushed by “hazards”: intense rain gusts in some regions and drought in others. Scientists have yet to elucidate these hazards. But they can have profound effects. A farmer can see his crop washed away by a thunderstorm or seedlings wither in a drought. In his part of Andhra Pradesh in south-eastern India, S. Ananth, a monsoon writer, says that this year the monsoon produced only one downpour and a few mild showers. A cyclone passed through the Bay of Bengal in May, which was unusually early. Mr Ananth’s great-grandfather used to say that after a cyclone in May, the monsoon would fail. Popular myth, perhaps, but local farmers are worried.

Since whims can make or break farmers, says Patil, Skymet uses satellite imagery and data from more than 7,000 weather stations to make 72-hour forecasts with village-level detail, including storm and drought alerts, which farmers can access on their phones. Millions of rural people use the service, which Patil says has done a lot to improve the accuracy of short-term forecasts.

Yet a long-term threat also looms: the monsoon effects of climate change. Recent analysis in the journal Earth system dynamics led by Anja Katzenberger of the Potsdam Institute for Climate Impact Research suggests that the monsoon is getting both wetter – by 5% for every degree Celsius of global warming – and more irregular. In other words, the frequency of extreme downpours is increasing. One would think that the aerosol soup of dust, exhaust emissions and thatch particles that hangs over the vast plains of northern India could absorb solar energy and thus somewhat counteract the effects on the monsoon d ‘a warming planet. Yet a paper in Earth Sciences Opinion led by Qinjian Jin of the University of Kansas argues that Asian dust more generally boosts an overhead heat pump that also helps make the monsoon warmer and wetter. While the monsoon has long made mankind in South Asia, man is now remaking the monsoon.

It is also not clear what can be done about it, unless there is a global desire to reduce carbon emissions. Building resilience helps. Work is underway in India to improve crop selection and management. Improving water storage and reducing the risk of flooding would also help. Here, however, aquifers are being tapped faster than rain can replenish them, while urban development engulfs centuries-old reservoirs, water reservoirs and floodplains. Meanwhile, India remains dependent on coal for electricity and spitting trucks and trains for transport. The monsoon will continue to bring relief but also, increasingly, sorrow.

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This article appeared in the Asia section of the print edition under the title “Wet winds of change”


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