• Disaster swept through the Himalayan village of Dharali on the way to Gangotri with a massive cloudburst leading to flash floods that barrelled through homes, trees, and cars, trapping 60-70 people and leaving at least four dead.

• Dharali village of Uttarkashi in Uttarakhand is the primary stopover on the way to Gangotri, the origin of the Ganges, and home to many hotels, restaurants, and home stays.

• At least half the village was buried under the fast flowing mudslide of slush, rubble and water on August 5.

• The devastating flashflood came in the wake of a cloudburst somewhere in the catchment area of the Kheer Ganga river.

• Uttarkashi is located at about 1,160 metres above sea level.

• The Indian Himalayas are considered vulnerable to unusual and extreme weather events, including cloudbursts, extreme precipitation, flash floods, and avalanches, the risk of all of which is said to increase as climate change intensifies.

What is cloudburst?

• Cyclones and cloudbursts cause flash floods and lead to huge losses. 

• Cloudbursts are counted as among the most devastating natural disasters in the Indian Himalayas, causing an enormous amount of rainfall across a limited area within an extremely short span of time.

• Cloudburst is a natural and common phenomenon in the Himalayas.

• Generally, cloudburst refers to particularly heavy precipitation in a short period of time over a limited geographical area.

• According to the India Meteorological Department (IMD), rain falling at a rate of over 100 millimetres an hour with strong winds and lightning across 20-30 square kilometres of area is termed a cloudburst.

• It is just as if the whole cloud has suddenly precipitated its moisture at once, as though it had been pricked and suddenly collapsed. 

• It is very difficult to predict the cloudbursts due to its very small scale in space and time. 

• Cloudbursts do occur at plains, however, mountainous regions are more prone to cloud bursts due to orography.

• Hilly areas in Himachal Pradesh, Uttarakhand, the northern areas of West Bengal, Sikkim, Arunachal Pradesh, Manipur, Mizoram, Meghalaya, Nagaland and Tripura and the coastal areas in the states of West Bengal, Odisha, Andhra Pradesh, Tamil Nadu, Karnataka, Kerala, Maharashtra and Gujarat and Union Territories of Andaman and Nicobar Islands and Lakhshadweep are more prone to such phenomena.

What are flash floods?

• Flash floods occur within six hours, mainly due to heavy rainfall associated with towering cumulus clouds, thunderstorms, tropical cyclones or during passage of cold weather fronts, or by dam failure or other river obstruction. 

• This type of flood requires a rapid localised warning system. 

• Flash floods occur due to high rate of water flow as also due to poor permeability of the soil. 

• Areas with hardpan just below the surface of the soil are more prone to floods as water fails to seep down to the deeper layers. 

• The construction of buildings, highways, driveways, and parking lots increases runoff by reducing the amount of rain absorbed by the ground. This runoff increases the flash flood potential. 

• During heavy rain, the storm drains can become overwhelmed or plugged by debris and flood the roads and buildings nearby. Low spots, such as underpasses, underground parking garages, basements, and low water crossings can become death traps.

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