Why In News?
Recent flash floods triggered by extreme rainfall in the Himalayan States have brought the severe disaster risks of cloudbursts into sharp national focus.
What is a Cloudburst?
A cloudburst is an extreme, highly localized rainfall event occurring over a very small area within a short period.
The India Meteorological Department (IMD) defines a cloudburst as 100 mm or more rainfall in one hour over an area of approximately 20–30 sq. km.
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Such intense rainfall often triggers flash floods and landslides, especially in mountainous regions.
Mini-Cloudburst: Although not officially recognized by IMD, several meteorological studies classify 50–100 mm rainfall in one hour over a similar area as a mini-cloudburst, as it can also cause severe damage in fragile Himalayan terrain.
Where are Cloudbursts Most Common in India?
Himalayan Region: The highest frequency of cloudbursts occurs along the southern Himalayas, particularly in Uttarakhand, Himachal Pradesh, Jammu & Kashmir, and Ladakh, where steep mountain slopes rapidly lift moisture-laden monsoon winds.
Western Ghats: The windward side of the Western Ghats, stretching from Goa to Gujarat (Saurashtra), is highly vulnerable as moisture-rich Arabian Sea winds undergo sudden orographic lifting, producing localized torrential rainfall.
North-Eastern Hills: Arunachal Pradesh, Sikkim, Meghalaya, and other northeastern hill states frequently experience cloudbursts because rugged terrain and deep valleys intensify convective activity and channel moist winds upward.
Why Do Cloudbursts Occur?
Orographic Effect: When warm, moisture-laden monsoon winds strike steep mountain ranges such as the Himalayas or Western Ghats, they are forced to rise rapidly.
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The rising air cools quickly, causing intense condensation and extremely heavy rainfall over a very small area.
Valley Funnelling: Narrow mountain valleys act like funnels, concentrating moist air into confined spaces and strengthening upward motion.
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This localized lifting often triggers cloudbursts, as observed in regions such as Kullu (Himachal Pradesh) and Garhwal (Uttarakhand).
Deep Convective Clouds: Strong surface heating creates towering Cumulonimbus clouds reaching 12–15 km in height.
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Powerful updrafts suspend large water droplets until they collapse, releasing enormous volumes of rain within minutes.
High Atmospheric Moisture: The interaction of the southwest monsoon with Western Disturbances or other upper-air systems increases atmospheric moisture, creating ideal conditions for explosive rainfall.
Strong Atmospheric Instability: High Convective Available Potential Energy (CAPE), abundant precipitable water, vertical wind shear, and slow-moving thunderstorms allow rain-bearing clouds to remain stationary over one location, leading to cloudbursts.