The monsoon is becoming more extreme

Like all of millions of small farmers whose lives depend on the annual monsoon, 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 Maharashtra's 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.

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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 50per 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 Gagre are experiencing: greater uncertainty.

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“The heavy rainfall events are increasing at a rapid pace,” said 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,” Koll said. “It can be a month’s rainfall or a week’s rainfall in a few hours to a few days.”

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,” Gagre said.

A Palace for the Clouds

In the 1870s, Sajjan Singh, the teenage ruler of the Mewar region in western India, ordered the construction of a marble palace on a rugged hill above the lake city of Udaipur. The monsoon for him was a source of fascination, and the new palace would be a fine place to watch the clouds roll in.

Sajjan Singh didn’t live to see it finished — he died at 26, perhaps, it’s been said, of drink — but the building was completed by his successor. Tourists, mostly from India’s burgeoning middle class, are drawn to it today, cramming into taxis for the winding, bumpy ride up the hill.

Known as the Monsoon Palace, its eastern side offers a sweeping view of Udaipur and its glistening waters. But in summer the view from the opposite side is equally spectacular: the approach of moisture-laden monsoon clouds, scudding across the sky.

Those clouds are borne on winds from the southwest. And for a long time, that was most of what was known about the monsoon — it was caused by a shift in the winds that occurred in late spring and continued through summer. At least as far back as the first century, sailors had learned to take advantage of these winds, riding them from the Middle East across the Indian Ocean and Arabian Sea to India.

It wasn’t until the 17th century that Edmond Halley, the English astronomer and meteorologist best known for the comet that bears his name, finally described the monsoon’s mechanism. The shift in the winds — the arrival of rain — was caused by seasonal changes in the relationship between ocean and land temperatures.

He was right. And remarkably, “His theory was entirely based on hearsay evidence,” said Ranjan Kelkar, a student of the monsoon who headed the India Meteorological Department from 1998 to 2003. “Halley had never come to India.”

By the time the Monsoon Palace was built, there was plenty of direct evidence. This was largely thanks to the British East India Co., which ruled the country for a century, until the mid-1800s. The company “did many bad things, but among the good things was that it set up rain gauges and observatories,” Kelkar said.

A succession of British, and later Indian, scientists divined more details of the monsoon, including how the rains occur as the moist ocean air hits the subcontinent, rises and cools, and the moisture condenses into raindrops.

Scientists now know that the monsoon is quite complex. Other theories of how it originates have been developed, including one that ties the monsoon to the northward shift of a zone of trade winds. But the basics, as Halley outlined, remain. An engine that drives it is the temperature difference between land and ocean.

In spring, as the Northern Hemisphere tilts toward the sun, the subcontinent heats faster than the ocean. As the air over the land warms, the air pressure drops, which draws in higher-pressure air from the ocean. “That temperature difference creates this pressure difference that drives this moisture-laden air from the ocean toward the land,” Koll said. The rotation of Earth gives these winds their direction.

But that’s only part of the story, said Anders Levermann, a climate scientist at the Potsdam Institute for Climate Impact Research in Germany. “The moment the first rain falls, the land gets cooled,” he said.

That would be expected to stop, or at least slow, the monsoon, by reducing the temperature difference between land and ocean. But there’s now another source of warmth over the land: the condensation of water vapor into droplets, which releases heat. That maintains the temperature difference and keeps the monsoon going.

This self-sustaining feature is important, Levermann said, because it suggests that, as the world keeps getting warmer, year-to-year variability of the monsoon could increase. “Once you have started the monsoon strong, it will become even stronger,” he said. “Once you have started the monsoon weak, it will become weaker.”

Over the centuries the subcontinent has experienced weak or “failed” monsoons, in which the overall amount of rain is 20 per cent-30 per cent lower than average. A failed monsoon in 1899 led to the deaths of 9 million people in central India, by some estimates.

In the middle of the 20th century, foreign aid helped India get through poor monsoons without famine. Since then, improvements in agriculture have made a big difference.