Context
Over the last three days, cloudbursts and flash floods have killed over 20 people in various parts of Himachal Pradesh and Uttarakhand.
Relevance
GS Paper 1:Important Geophysical phenomena such as earthquakes, tsunamis, Volcanic activity, cyclones etc.
Mains Question
Discuss the measures to prevent and mitigate the devastating effects of cloudbursts, highlighting the causes and consequences of cloudbursts. (250 Words)
CloudBurst
- A cloudburst is a brief but intense burst of rain. Short bursts of extremely heavy rain over a small geographical area can cause widespread devastation.
- However, not all instances of extremely heavy rainfall are cloudbursts. A cloudburst is defined very precisely.
- A cloudburst event is defined as rainfall of 10 cm or more in an hour over a 10 km x 10 km area.
- According to this definition, 5 cm of rain in a half-hour period over the same area is also considered a cloudburst.
Cloudburst Occurrence
- It happens when moist air moves up a hill, forming a vertical column of clouds known as ‘cumulonimbus’ clouds.
- Such clouds are known to produce rain, thunder, and lightning. An orographic lift is the upward motion of the clouds.
- When these unstable clouds become heavy enough and become trapped in the ridges and valleys between the hills, they cause an intense rainstorm over a small area.
- The energy required for the cloudburst is derived from the upward motion of air.
- It is most common between 1,000 and 2,500 metres above sea level.
- The moisture is typically provided by a low-pressure system (associated with cyclonic storms in the ocean) over the Gangetic plains, which is accompanied by low-level winds from the east.
- Cloudbursts are sometimes aided by winds blowing in from the north-west.
- Cloudburst events are highly unlikely due to the numerous factors that must come together.
What is the frequency of cloudbursts?
- Cloudbursts are a common occurrence, especially during the monsoon season.
- The majority of these occur in Himalayan states due to the local topology, wind systems, and temperature gradients between the lower and upper atmosphere.
The result of a cloudburst
- Because of the terrain, heavy rainfall events frequently cause landslides and flash floods, wreaking havoc downstream.
- These occur in very small areas that are frequently devoid of rainfall measuring instruments. However, the consequences of these events are not limited to small areas.
Cloudburst forecasting
- The India Meteorological Department (IMD) forecasts rainfall events months in advance, but it does not predict the amount of rainfall — no meteorological agency does.
- Rainfall forecasts can be light, heavy, or very heavy, but weather scientists cannot predict how much rain will fall in any given location.
- In addition, forecasts are typically for a relatively large geographical area, such as a region, a state, a meteorological subdivision, or, at best, a district.
- Forecasts for smaller areas become increasingly uncertain.
- It is also theoretically possible to forecast rainfall over a very small area.
- It necessitates a dense network of weather instruments as well as computing capabilities that appear to be unattainable with current technologies.
- As a result, specific cloudburst events are impossible to predict.
Are cloudbursts becoming more common?
- There is no long-term trend indicating that cloudbursts, as defined by the IMD, are on the rise.
- However, incidents of extreme rainfall, as well as other extreme weather events, are on the rise — not just in India, but globally.
- While India’s overall rainfall has not changed significantly, an increasing proportion of rainfall is occurring in a short period of time.
- This means that even during the rainy season, the wet spells are very wet and are interspersed with long dry spells.
- This type of pattern, attributed to climate change, suggests that cloudburst events may be on the rise as well.
