Why monsoon rains have been so deadly in India this year

Heavy rainfall in several parts has caused landslides and floods, killing hundreds

India's monsoon has turned wild.

Half of the country is reeling under floods after extraordinary downpours, with Punjab facing its worst deluge since 1988.

Some parts of Punjab, Haryana and Rajasthan saw rains more than 1,000% above normal in just 24 hours, the Indian Meteorology Department (IMD) says.

Between 28 August and 3 September, rainfall in northwest India was 180% above average, and in the south, it was 73%.

More heavy rain is forecast across large parts of the country this week.

The rains have caused landslides and floods in several parts of the country, inundating villages and towns and killing hundreds.

But how did the rainfall become so intense?

Changing monsoon

The climate crisis is changing the behaviour of the monsoon.

Scientists say one of the main changes is that there is a much higher amount of moisture in the air now, from both the Indian Ocean and the Arabian due to warmer climate.

Also, in the past, monsoon rains were steady and spread evenly over the four months - June, July, August and September. But meteorologists say they have observed that rains now often fall in huge volumes within a small area in a short span of time after a prolonged dry spell.

Experts say this is increasingly happening in the mountainous regions where massive moisture-laden clouds hit the hills, pouring huge amounts of rain very quickly in a small area - a phenomenon that is known as cloudburst.

This was one of the main causes for the havoc in the Himalayan states of Uttarakhand, Indian-administered Kashmir and Himachal Pradesh during the first week of August.

But the reasons change as you start travelling down south from the Himalayan states.

Westerly disturbances

In August, prolonged heavy and even extremely heavy rainfall lashed states like Punjab and Haryana for days.

Meteorologists say it was mainly because of the interaction between the already existing monsoon system in the Indian subcontinent and westerly disturbances, a low pressure system that originates in the Mediterranean region and travels eastward.

This westerly disturbance often carries a mass of cold air from the upper levels of the atmosphere and when it meets the relatively warmer and moisture-laden air in lower levels - like the current monsoon has - it can lead to intense weather activity.

"It's the result of a rare 'atmospheric tango' between the monsoon and the westerly disturbance," said Akshay Deoras, a research scientist with the department of meteorology at University of Reading in the UK.

"Think of the monsoon as a loaded water cannon, and western disturbances as the trigger," he explained. This trigger, he said, was pulled with force, drenching several northern states.

IMD has also confirmed that the extreme rainfall for a sustained period in northern India and other parts of the country was mainly because of the clash of the monsoon system and the westerly disturbances.

"Such interactions during the peak monsoon season are uncommon since western disturbances typically retreat northward during this time," said Mr Deoras.

So, why did it detour towards the east this year?

Scientists put that down to jet streams - narrow, fast-flowing currents of air in the upper atmosphere that travel from west to east around the globe. They say that global warming is making these currents increasingly "wavier", which means it's meandering and not following a steady path. And that influences other weather systems too.

Studies have shown that wavy jet streams are leading to extreme weather events around the world, including in India recently, where the subtropical jet stream steered the westerly disturbances unusually far south into northern parts.

"It is a vivid reminder of how global wind patterns can supercharge local monsoon dynamics, turning the monsoon into mayhem, rivers into raging torrents and the Himalayas into a graveyard," said Mr Deoras.

Half of the country is reeling under floods after extraordinary downpours, with Punjab facing its worst deluge since 1988

Unstable mountains

Extreme rainfalls during the ongoing monsoon season are a major source of floods in several parts of India. But other factors play a role too - particularly when it comes to flash-floods and landslides.

Several parts of northern India and Pakistan, which are downstream from the rivers originating in the Himalayas, have seen devastating floods even when there were no cloudbursts or significant rainfall.

Scientists offer several possible explanations - such as bursting of over-filled glacial lakes due to rapid melting of glaciers, swelling of underground lakes that open up through cracks, and landslides blocking rivers creating artificial lakes that then unleash floods.

While the exact reasons are yet to be established, experts say mountains are becoming unstable with fast melting glaciers, snow-fields, snowpacks and permafrost (permanent frozen ground that remains hidden under the soil) due to global warming.

The ice and snow act like cement to keep mountain slopes stable.

And rains play a spoilsport here as well.

Experts say that global warming means that rains are increasingly being reported in higher reaches where it mostly snowed in the past, destabilising mountains further with water percolating and loosening the ground.

"We are seeing entire snowfields melting within a day or two when rains fall on them and the huge quantity of water gushes down as floods," said Jakob Steiner, a geoscientist with University of Graz.

Man-made disasters

These factors are further complicated by human activities. Human settlements have encroached paths of rivers and floodplains, both in the mountains and plains, blocking their way.

Rampant infrastructure development such as highways, tunnels and hydropower plants further weaken the mountains.

Despite warning of an above-normal monsoon rainfall this year, river-embankments and age-old drains in many places remain unrepaired, while plastic waste clogs waterways meant to reduce urban floods.

Experts say these issues must be addressed timely to minimise the impacts and losses caused by rains and floods.

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