Cloudbursts are causing chaos in mountainous parts of India and Pakistan, with tremendous amounts of rain falling in a short period of time over a concentrated area. The intense, sudden deluges have proved fatal in both countries.
As many as 300 people died in one northwestern Pakistani district, Buner, after a cloudburst. The strength and volume of rain triggered flash flooding, landslides and mudflows. Boulders from steep slopes came crashing down with the water to flatten homes and reduce villages to rubble.
The northern Indian state of Uttarakhand had a cloudburst earlier this month. Local TV showed floodwaters surging down a mountain and crashing into Dharali, a Himalayan village. In 2013, more than 6,000 people died and 4,500 villages were affected when a similar cloudburst struck the state.
Here’s what to know about cloudbursts:
They are complex and extreme weather events
A cloudburst occurs when a large volume of rain falls in a very short period, usually more than 100 millimeters (about 4 inches) within an hour over a localized area, around 30 square kilometers (11.6 square miles).
Cloudbursts are sudden and violent, with devastating consequences and widespread destruction, and can be the equivalent of several hours of normal rainfall or longer. The event is the bursting of a cloud and the discharge of its contents at the same time, like a rain bomb.
Several factors contribute to a cloudburst, including warm, moist air rising upward, high humidity, low pressure, instability and convective cloud formation.
Moist air is forced to rise after encountering a hill or mountain. This rising air cools and condenses. Clouds that are large, dense and capable of heavy rainfall form.
Hills or mountains act like barriers and often trap these clouds, so they cannot disperse or move easily. Strong upward currents keep moisture suspended inside the clouds, delaying rainfall.
When the clouds cannot hold the accumulated moisture anymore, they burst and release it all at once.
India and Pakistan have ideal conditions
Cloudbursts thrive in moisture, monsoons and mountains. Regions of India and Pakistan have all three, making them vulnerable to these extreme weather events.
The Himalayas, Karakoram and Hindu Kush mountain ranges are home to the world’s highest and most famous peaks, spanning multiple countries including India and Pakistan.
The frequency of cloudbursts in these two South Asian nations has been steadily rising due to a warming atmosphere, because a warmer air mass can hold more moisture, creating conditions for sudden and intense downpours.
The South Asian region has traditionally had two monsoon seasons. One typically lasts from June to September, with rains moving southwest to northeast. The other, from roughly October to December, moves in the opposite direction.
But with more planet-warming gases in the air, the rain now only loosely follows this pattern.
This is because the warmer air can hold more moisture from the Arabian Sea and Indian Ocean, and that rain then tends to get dumped all at once. It means the monsoon is punctuated with intense flooding and dry spells, rather than sustained rain throughout.
The combination of moisture, mountains and monsoons force these moisture-laden winds upward, triggering sudden condensation and cloudbursts.
They are hard to predict, but precaution is possible
It’s difficult to predict cloudbursts because of their size, duration, suddenness and complex atmospheric mechanisms.
Asfandyar Khan Khattak, a Pakistani official from the northwest province of Khyber Pakhtunkhwa, said there was “no forecasting system anywhere in the world” that could predict the exact time and location of a cloudburst.
The Pakistani government said that while an early warning system was in place in Buner district, where hundreds of people died after a cloudburst, the downpour was so sudden and intense that it struck before residents could be alerted.
Community organization SOST, which is also the name of a border village in Pakistan’s northern Gilgit-Baltistan region, says precautions are possible.
It advises people to avoid building homes right next to rivers and valleys, to postpone any travel to hilly areas if heavy rain is forecast, to keep an emergency kit ready, and to avoid traveling on mountainous roads during heavy rain or at night.
It recommends afforestation to reduce surface runoff and enhance water absorption, and regular clearing and widening of riverbanks and drainage channels.
Climate change is fueling their frequency
Experts say cloudbursts have increased in recent years, partly due to climate change, while damage from associated storms has also increased due to unplanned development in mountain areas.
Climate change has directly amplified the triggers of cloudbursts in Pakistan, especially. Every 1°C rise allows the air to hold about 7% more moisture, increasing the potential for heavy rainfall in short bursts.
The warming of the Indian Ocean and Arabian Sea pushes more moisture into the atmosphere. Melting glaciers and snow alter local weather patterns, making rainfall events more erratic and extreme. Environmental degradation, in the form of deforestation and wetland loss, reduces the land’s ability to absorb water, magnifying flash floods.
Climate change has been a central driver in the destruction seen in Pakistan’s northern areas.
“Rising global temperatures have supercharged the hydrologic cycle, leading to more intense and erratic rainfall,” said Khalid Khan, a former special secretary for climate change in Pakistan and chairman of climate initiative PlanetPulse.
“In our northern regions, warming accelerates glacier melt, adds excessive moisture to the atmosphere, and destabilizes mountain slopes. In short, climate change is making rare events more frequent, and frequent events more destructive.”
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Associated Press writers Munir Ahmed and Riaz Khan contributed to this report from Islamabad and Peshawar, Pakistan, respectively.
