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What is Flash Floods?

Context:

The 2023 Monsoon rain in Himachal Pradesh has brought severe Flash Floods in many regions causing unprecedented loss of lives and assets.

Relevance:

GS I: Geography

Dimensions of the Article:

  1. Flash Floods: Sudden and Destructive Water Events
  2. Differences Between Flash Floods and General Floods

Flash Floods: Sudden and Destructive Water Events

  • Flash floods are rapid and unexpected floods that occur within a short time, usually hours, following heavy rainfall or intense water accumulation events.
  • The National Weather Service in the United States defines flash floods as floods caused by rainfall within a duration of less than 6 hours.
  • They are characterized by a swift rise in water levels in rivers, streams, or urban areas, often catching people off guard.
Causes:
  • Heavy rainfall is the primary cause of flash floods, but they can also result from dam or levee failures, ice or debris jams, or sudden release of water from natural reservoirs.
  • In India, flash floods are often associated with cloudbursts, which are sudden and intense rainfall episodes.
Factors Contributing to Flash Floods:
  • Intensity and duration of rainfall, steepness of terrain, soil conditions, and the presence of man-made structures affecting water flow can contribute to flash floods.
Features:
  • Flash floods are characterized by their powerful force and velocity, carrying large volumes of water, debris, and sediment.
  • Drainage systems can become overwhelmed, rivers may overflow their banks, and low-lying areas can be inundated.
  • Flash flooding is more common in narrow and steep river systems, as the water flows rapidly.
  • Urban areas located near small rivers are susceptible to flash floods due to the inability of hard surfaces to absorb water.

Differences Between Flash Floods and General Floods:

Flash Floods:
  • Rapid onset, occurring within a short span of time (hours or minutes).
  • Short-lived events that subside quickly after the intense rainfall or water accumulation ends.
  • High intensity with a sudden surge of water, resulting in significant destruction.
  • Little to no warning time, happening rapidly and often catching people off guard.
  • Localized events, usually occurring in specific areas where intense rainfall or other factors lead to rapid water accumulation.
General Floods:
  • Develop gradually over a longer period (days or weeks) due to sustained rainfall or melting snow.
  • Longer duration, lasting for days, weeks, or even months.
  • Lower peak intensity compared to flash floods due to the slower rise in water levels.
  • More advance warning, allowing for evacuation plans and emergency measures to be implemented.
  • Can cover larger areas, including river basins, coastal regions, or expansive low-lying areas.

-Source: The Hindu


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