When Is High Rainfall Termed As A ‘Cloudburst’?

Context: 

Recently, following heavy rains in Himachal Pradesh, landslides have occurred in the state and the Chief Minister of the state said that reports of cloudbursts have also emerged. 

About Cloudburst:

• A Localized Event with intense rainfall activity.
• Occurrence: While the phenomenon can also occur in plains, it is most common in hilly regions.
• Specific Definition: Rainfall of 10 cm or more in an hour over a roughly 10 km x 10 km area.
  • By this definition, 5 cm of rainfall in a half-hour period over the same area would also be categorized as a cloudburst.
• Amount of Received Rainfall: During a cloudburst event, a place receives about 10% of the annual rainfall within an hour.

Rainfall in India:

• Amount of Received Rainfall: In a normal year, India, as a whole, receives about 116 cm of rainfall over the entire year.
• High Geographical Variations: There are huge geographical variations in rainfall within the country, and some areas receive over 10 times more than that amount in a year.

How Common are Cloudbursts?

• Common Events: These are common events, particularly during the monsoon months. 
• Occurrence in the Himalayan States: The local topology, wind systems, and temperature gradients between the lower and upper atmosphere facilitate the occurrence of such events.
• Role of Measuring Instruments: They take place in very small areas which are often devoid of rainfall-measuring instruments. 

Associated Concerns: 

• Consequences: The consequences of these events are not confined to small areas.
• Large Destruction: Because of the nature of the terrain, the heavy rainfall events often trigger landslides and flash floods, causing extensive destruction downstream. 
• Not Specific Treatment Recognition in General: Every sudden downpour that leads to the destruction of life and property in the hilly areas gets described as a “cloudburst”. 
• Unrecorded Events: It is also possible that actual cloudburst events in remote locations aren’t recorded.

About Forecasting of Cloudbursts:

• Predictability: 
  • Rainfall Events: There are warnings for heavy to very heavy rainfall events, and these are routinely forecast four to five days in advance. 
    • The possibility of extremely heavy rainfall, which could result in cloudburst-like situations, is forecast six to 12 hours in advance.
  • Quantum of Rainfall: No meteorological agency can predict the quantum of rainfall and specific cloudburst events.
    • There are forecasts for a relatively large geographical area, at best at a district level. As they zoom in over smaller areas, the forecasts get more and more uncertain. 
• Lacking Technology: Theoretically, it is possible to forecast rainfall over a very small area as well, but it requires a very dense network of weather instruments, and computing capabilities that seem unfeasible with current technologies.

Increase in Cloudburst Incidents:

• There is no such long-term trend suggested by the Indian Meteorological department (IMD).
• However, incidents of extreme rainfall, like other extreme weather events, are increasing across the world.

Challenges Need to be Tackled and Prepared: 

• Rapid Onset and Intensity
• Flash Flooding 
• Infrastructure Vulnerability
• Landslides and Mudslides 
• Communication Disruptions 
• Humanitarian Impact 
• Environmental Degradation 
• Limited Forecasting and Prediction

The Path Ahead: 

• Improvement of Drainage Infrastructure 
• Improvement of Early Warning Systems 
• Adequate and Sustainable Urban Planning and Land Use 
• Climate Change Adaptation 
• Public Awareness and Education 
• Infrastructure Upgrades 
• Emergency Response Preparedness 
• Research and Innovation 

News Source: The Indian Express