This monsoon season, massive, sudden downpours known as cloudbursts have hit Pakistan and India, causing flash floods and landslides that have killed hundreds of people.
What are cloudbursts and why do they happen?
According to a widely accepted definition, a cloudburst is when more than 100mm (4 inches) of rain falls in one hour over a small area.
This year, the monsoon, which originates in the Bay of Bengal and moves westward across northern India to Pakistan every summer, has brought deadly cloudbursts.
Weather studies show that in South Asia, cloudbursts typically occur when warm, moisture-laden monsoon winds meet cold mountain air in northern India and Pakistan, causing condensation. With a warming planet, the monsoon air is hotter and can hold more moisture.
Data from India’s weather department indicates that cloudbursts are most common in the Himalayan regions of Indian Illegally Occupied Jammu and Kashmir (IIJK), Ladakh, Himachal Pradesh, and Uttarakhand.
Fahad Saeed, a senior climate scientist at Berlin-based Climate Analytics, explained that in the mountains of northern Pakistan, the warm monsoon system from the east is meeting colder air from the west, originating from the subtropical jet stream—a high-altitude weather system from the Mediterranean.
He said that global warming is pushing this jet stream further south in the summer, where it can now combine with the lower-level clouds of the monsoon in Pakistan, forming a tower of clouds that generates intense rain.
Similar intense rainfall, though triggered by different local factors, occurs worldwide, such as the floods in Texas in July, where more than 300mm of rain fell in less than an hour, creating a wall of water down the Guadalupe River.
Why Is the Region Hit So Badly by Cloudbursts?
This monsoon season has seen at least four major deadly cloudbursts, including one in Uttarakhand, India, where video captured village buildings being swept down a mountain, and another in Buner, Pakistan’s Hindu Kush mountain range, where over 200 people died after at least 150mm of rain fell in an hour.
S.D. Sanap, a scientist with the India Meteorological Department’s Pune office, said such cloudbursts are becoming more frequent in the western Himalayas, which span India and Pakistan, but it’s difficult to pinpoint a single cause for the increase.
Moetasim Ashfaq, a US-based weather expert, said that the cloudbursts on both sides of the border were triggered in the same way: very moist monsoon air, upslope winds, and storms that stalled over valleys.
Pradeep Dangol, a senior hydrology research associate at the International Centre for Integrated Mountain Development in Nepal, explained that if a cloudburst happens over flat land, the rainfall spreads out over a wide area, making the impact less severe.
However, in steep mountain valleys, the rain is concentrated into narrow streams and slopes, which can trigger flash floods and landslides, he said.
Can Cloudbursts Be Predicted?
Forecasting such events days in advance is nearly impossible, though radars can track the formation of dense clouds and provide short-term warnings of intense downpours, Sanap said.
To improve monitoring, the India Meteorological Department has installed new radars across the Himalayas and set up observatories aimed at enhancing early warnings and understanding of these extreme weather events.
Syed Muhammad Tayyab Shah, who leads risk assessment at Pakistan’s National Disaster Management Authority, said it is possible to warn about the general area but not to pinpoint the exact location where a cloudburst will occur.
