KUMBHARWADI - Like all of India's tens of millions of small farmers whose lives depend on the annual monsoon, Mr Bhagwat Gagre keeps a firm eye on the sky.

At his 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 Gagre's tiny farm in Kumbharwadi and ensuring that the crops he and his wife sow will 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.

At Gagre's farm in late August, dryness was the problem - the monsoon had begun to feel all but absent. "If we don't get rain in the next 15 or 20 days," he said, gesturing to his fields, "productivity will go down 50 per cent."

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 like Mr Gagre 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.

But the monsoon is much more than rain - it's a collective mood, a shared experience across communities and across time, and deeply ingrained. Artists and poets have tried to capture it for centuries. Novelists use it as a plot device, and it provides rainy, romantic interludes in countless Bollywood movies. And the monsoon is an economic force, particularly for the small farmers who get three-quarters, or more, of their annual rainfall from it.

A good monsoon can bring plenty; a bad monsoon, hardship. And in the past, a terrible monsoon could bring famine.

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."

Mr Gagre farms in a drylands region. Because he lives in the shadow of the Ghats, the monsoon brings less rain - the mountains wring most of the moisture from the clouds before it can reach his farm. For him, 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.

And if the trenches and other water-conservation efforts had not worked? "Nobody would be living here today," Mr Gagre said. NEW YORK TIMES