Monsoon in South Asia is becoming more extreme
India’s tens of millions of small farmers whose lives depend on the annual monsoon keep a firm eye on the sky. At a village in the shadow of the Western Ghats mountain range, the rainy season usually starts in June. Winds over the subcontinent reverse, as they have for millennia, carrying clouds ripe with water from the Arabian Sea up over the Ghats, soaking farms and ensuring that crops have the rain they need.
Now, however, across South Asia, climate change is making the monsoon more erratic, less dependable and even dangerous, with more violent rainfall as well as worsening dry spells. For a region home to nearly one-quarter of the world’s population, the consequences are dire.
In other parts of South Asia, the problem was too much rain, too quickly. Pakistan, to India’s northwest, was struck by relentless downpours, leaving much of the nation underwater and killing at least 1,500 people. In Bengaluru, India’s tech capital, devastating rains in early September forced workers to use boats instead of cars in the streets.
Scientists blame global warming from the burning of fossil fuels for the changes in the monsoon. Computer models suggest that as this warming continues, the monsoon will strengthen, with more rain overall.
But the scientists also see what farmers are experiencing: greater uncertainty.
“The heavy rainfall events are increasing at a rapid pace,” said Dr Roxy Mathew Koll, a climate scientist at the Indian Institute of Tropical Meteorology in Pune. “That is a very, very clear shift that we see in monsoon patterns.”
The monsoon season is defined by patterns. It begins on India’s west coast with a springtime reversal of winds, pushing moisture-laden air from the Arabian Sea toward land. Then, from the Bay of Bengal to the east, winds start carrying more rain across the subcontinent.
Through July and August, the rains march northward in fits and starts. In September the monsoon retreats for another year.
The monsoon is becoming more erratic because of a basic bit of science: Warmer air holds more moisture. The moisture accumulates in the atmosphere and can stay there longer, increasing the length of dry spells. But then, when it does rain, “it dumps all that moisture in a very short time,” Dr Koll said. “It can be a month’s rainfall or a week’s rainfall in a few hours to a few days.”
Farms in the shadow of the Ghats are in drylands regions because the monsoon brings less rain, the mountains wring most of the moisture from the clouds before it can reach the farm. Longer dry spells are a big threat.
To cope, villagers have dug long, meandering trenches by hand along the hillsides, the better to catch the rain that falls, prevent it from running off into streams and give it time to soak into the ground. That has helped keep local wells from drying up after the monsoon is over.