Cloudburst & Flash Floods


    In Context

    • Recently cloudbursts and flash floods were seen in different parts of Himachal Pradesh and Uttarakhand.

    More about the news

    • Isolated areas in these two states have reported heavy rainfall during this time. 
      • The rainfall triggered landslides and flash floods that have disrupted rail and road traffic and resulted in house and wall collapses.
    • Himachal Pradesh was hit by 29 cloudburst incidents in the last three years.

    What are Cloudbursts?

    • About:
      • A cloudburst is a localised but intense rainfall activity. 
      • Short spells of very heavy rainfall over a small geographical area can cause widespread destruction, especially in hilly regions where this phenomenon is the most common.
    • Definition:
      • Not all instances of very heavy rainfall, however, are cloudbursts. 
      • A cloudburst has a very specific definition: Rainfall of 10 cm or more in an hour over a roughly 10 km x 10-km area is classified as a cloudburst event. 
        • By this definition, 5 cm of rainfall in a half hour period over the same area would also be categorized as a cloudburst.
      • During a cloudburst event, a place receives about 10% of this annual rainfall within an hour. 
    • Frequency of Cloudbursts:
      • Cloudbursts are not uncommon events, particularly during the monsoon months. 
      • Most of these happen in the Himalayan states where the local topology, wind systems, and temperature gradients between the lower and upper atmosphere facilitate the occurrence of such events.
      • Are cloudburst incidents increasing?
        • There is no long-term trend that suggests that cloudbursts, as defined by the IMD, are rising. 
        • What is well established, however, is that incidents of extreme rainfall, as also other extreme weather events, are increasing — not just in India but across the world. 
        • While the overall amount of rainfall in India has not changed substantially, an increasing proportion of rainfall is happening in a short span of time. 
        • That means that the wet spells are very wet, and are interspersed with prolonged dry spells even in the rainy season.
    • Consequences:
      • Flash floods are mostly the result of cloudbursts.
      • Even if cloudburst & flash floods is a localised activity, the consequences of these events, are not confined to the small areas. 
      • Because of the nature of terrain, the heavy rainfall events often trigger landslides and flash floods, causing extensive destruction downstream. 

    Flash Floods

    • A flash flood is a rapid flooding of low-lying areas: washes, rivers, dry lakes and depressions.
      • Flash-floods are mostly the result of cloudbursts or blockage of river channel due to landslides.
    • The flood problem in the state is mainly during the months of June to August when the southwest monsoon is in progress and snow is melting in the higher reaches.


    • Death or Serious Injury
      • The very nature of flash floods makes them fast and very difficult to predict.
      • Since they can occur without warning, it is no surprise that people can be seriously injured or killed by these natural disasters.
    • Immediate Property Damage
      • In addition to the force of the water, flash floods can carry large debris such as boulders. 
      • This combination can cause heavy structural damage to homes making them uninhabitable and can carry away large pieces of property such as vehicles.
    • Loss of Critical Infrastructure
      • Large debris and flood waters can cause structural damage to bridges and roadways, making travel impossible.
      • Power, telephone, and cable lines can be taken out by flash floods as well.
      • Flood waters can disrupt or contaminate groundwater, making tap water unfit for consumption.
    • Deposited Sediment & Silt
      • Floods can leave behind large amounts of silt and other debris that can make travel difficult and can be costly to remove. 
    • Uninsured or Under-insured Homeowners
      • Being infrequent and unpredictable, many homeowners do not consider flash floods when insuring their homes.
    • Economic Losses
      • Depending on the damage caused, it may prevent local businesses from opening or keep customers from getting to those businesses.

    Initiatives in this direction

    • Flash Flood Guidance Services:
      • It is a robust system designed by the India Meteorological Department (IMD) to provide the necessary products in real-time to support the development of warnings for flash floods about 6-12 hours in advance at the watershed level for the flash flood-prone South Asian countries viz. India, Nepal, Bhutan, Bangladesh, and Sri Lanka.
    • South Asian Flash Flood Guidance System (FFGS):
      • The India Meteorological Department (IMD) launched the South Asian FFGS.
      • It is aimed at helping disaster management teams.
      • Helps governments make timely evacuation plans ahead of the actual event of flooding. 

    Source: IE