Uttarkashi cloudburst: How clouds dump over a billion litres of rain in a minute

India Today

2 days ago

A cloudburst led to flash floods in the high-altitude villages of Dharali in Uttarakhand's Uttarkashi district on Tuesday with several houses being damaged or swept away in the raging waters, according to people in the area. At least four people have died and over 50 are missing.The cloudburst took place in the catchment area of the Kheer Ganga river, leading to the devastating floods, locals said.advertisementWHAT IS A CLOUDBURST?A cloudburst is an extreme weather event characterized by an intense and sudden downpour of rain, typically measuring 100 millimeters (10 centimeters) or more within a very short period, often less than an hour, over a small geographical area of approximately 20 to 30 square kilometers.
This deluge of water can lead to devastating consequences such as flash floods, landslides, and severe damage to infrastructure, especially in mountainous regions.Cloudbursts are most common in hilly or mountainous terrain, such as the Himalayas, where warm, moist air is forced to ascend steep slopes in a process known as orographic lifting. As this air rises, it cools and condenses to form clouds. When the atmosphere can no longer hold the moisture, a rapid and heavy rainfall occurs.Strong upward air currents within thunderclouds keep raindrops suspended longer, allowing them to combine and grow larger—a process called the Langmuir precipitation mechanism. When the upward currents weaken suddenly, all the accumulated water falls rapidly, causing the intense rainfall characteristic of cloudbursts.Besides orographic lifting, cloudbursts can be triggered when warm air masses mix with cooler air, leading to sudden condensation. In monsoon-affected regions like the Indian subcontinent, moist winds from the Bay of Bengal or Arabian Sea travel across the plains and accumulate moisture.Upon hitting the Himalayan foothills, these winds are forced upward, amplifying cloudburst risks.The sheer volume of water in a cloudburst is staggering. For instance, 100 millimeters of rain over one square meter equates to 100 liters of water. Multiplied over a small hilly area, this can result in billions of liters of water unleashed in minutes, overwhelming rivers and drainage systems.Due to their localised and sudden nature, cloudbursts are notoriously difficult to predict, posing a significant challenge for early warning systems.Their impacts, flooding, landslides, and destruction, have caused severe humanitarian and economic losses in mountainous regions globally, with notable recent events in the Himalayas.Understanding cloudbursts is crucial to improving disaster preparedness and mitigating their devastating effects on vulnerable communities.According to the latest reports, about 10-12 people could be buried under the debris of the Uttarkashi cloudburst. Reportedly, 20-25 hotels and homestays may have been washed away.- EndsMust Watch