Question- Explain the mechanism and occurance of cloudbrust in the context of Indian subcontinent. Discuss two recent examples. UPSC CSE Main 2022 GS Paper 3.
Answer
A cloudburst is a sudden and intense rainfall event that can cause flash floods, landslides, and damage to life and property. A cloudburst is defined as rainfall of 10 cm or more in an hour over a small area. Cloudbursts are more common in hilly regions where the local topography, wind systems, and temperature gradients can create favourable conditions for the formation of such events. Some of the aspects of cloudbursts in the context of Indian subcontinent are:
Mechanism: Cloudbursts are caused by the rapid condensation of water vapour in clouds that are already saturated with moisture. In India, cloudbursts often occur during the monsoon season, when the southwesterly monsoon winds bring in copious amounts of moisture inland. The moist air that converges over land gets lifted as they encounter the hills. The moist air reaches an altitude and gets saturated, and the water starts condensing out of the air forming clouds. The clouds grow vertically and horizontally, forming cumulonimbus clouds that can extend up to 15 km in height. The clouds become unstable due to the difference in temperature and pressure between the upper and lower layers. The instability triggers strong updrafts and downdrafts within the clouds, which can cause the cloud droplets to collide and coalesce into larger raindrops. The raindrops become too heavy to be supported by the updrafts and fall rapidly to the ground as a cloudburst.
Occurrence: Cloudbursts are not very frequent events, but they can occur anywhere in India, especially in the Himalayan states such as Uttarakhand, Himachal Pradesh, Jammu and Kashmir, Sikkim, and Arunachal Pradesh. They can also occur in other hilly regions such as Western Ghats, Eastern Ghats, Vindhya Range, Satpura Range, etc. Cloudbursts usually occur between June and September, when the monsoon is active over India. They can also occur during pre-monsoon and post-monsoon seasons due to local weather systems such as thunderstorms, cyclones, low-pressure areas, etc. Cloudbursts are more likely to occur during the afternoon or evening hours when the solar heating is maximum and the atmospheric instability is high.
Examples: Some of the recent examples of cloudbursts in India are:
Uttarakhand 2021: On July 27, 2021, a series of cloudbursts hit several parts of Uttarakhand, causing flash floods, landslides, and damage to houses and roads. At least 14 people were killed and several others were injured or missing due to the cloudbursts. The worst affected districts were Pithoragarh, Chamoli, Tehri Garhwal, Rudraprayag, Uttarkashi, and Bageshwar.
Himachal Pradesh 2021: On August 11-12, 2021, several cloudbursts occurred in different parts of Himachal Pradesh, triggering flash floods, landslides, and destruction of infrastructure. At least 25 people were killed and over 40 were reported missing due to the cloudbursts. The most affected districts were Lahaul-Spiti, Kullu, Chamba, Kangra, Mandi, Shimla, and Kinnaur.