Flood

Flooding is an overflowing of water onto land that is normally dry (NOAA). There are various categories of floods. Coastal flooding is most frequently the result of storm surges and high winds coinciding with high tides (WMO, 2011).

A flash flood is a flood of short duration with a relatively high peak discharge in which the time interval between the observable causative event and the flood is less than four to six hours (WMO, 2006). A fluvial flood is a rise, unusually brief, in the water level of a stream or water body to a peak from which the water level recedes at a slower rate (WMO, 2012). A ‘glacial lake outburst flood’ is a phrase used to describe a sudden release of a significant amount of water retained in a glacial lake, irrespective of the cause (Emmer, 2017).

Floods affect more people than any other hazard. Worldwide, nearly 200 million live in coastal zones at risk of flooding. Flooding is usually the result of heavy or continuous rain that exceeds the absorptive capacity of the soil and the flow capacity of rivers, streams and coastal areas. Floods can be triggered by thunderstorms, tornadoes, tropical cyclones, monsoons, melting snow and dam breaks. The most common floods are flash floods, snowmelt floods, coastal floods and river floods. Flash floods and sudden floods are the most dangerous, especially when they occur at night.

Integrated Flood Management (IFM) is a process that promotes an integrated, rather than fragmented, approach to flood management. It integrates land and water resources development in a river basin, within the context of Integrated Resources Management, with a view to maximising the efficient use of floodplains and to minimising loss of life and property. IFM, like Integrated Water Resources Management, should encourage the participation of users, planners and policymakers at all levels (APFM).

Risk factors

  • Rapid population growth.
  • Rapid urbanization.
  • Environmental degradation: loss of forests and natural flood buffers.
  • Climate change will expose more people to future floods.
  • Melting glaciers and rising sea levels will bring floods to places not previously at risk.

Vulnerable areas

  • Developing countries are most at risk.
  • Although Asia remains the continent most hit by floods, Africa and Latin America are also heavily affected.
  • The poor, with the least means to adapt are often forced to live in high-risk places: slopes, flood plains, ravines, or in crowded, urban low-lying areas in mega-cities.

Risk reduction measures

  • Integrate flood risk assessment into urban planning strategies.
  • Avoid building on flood-prone land.
  • Develop new building codes to reinforce flood resistance.
  • Create more space for rivers, floodplains and wetlands.
  • Ensure health of coastal reefs and mangrove plantations.
  • Maintain early warning systems, backed up by regular drills and evacuation exercises.
  • Have an evacuation plan for those at risk, including the elderly, disabled and very young.
  • Catalyse finance and insurance schemes to protect assets and livelihoods.
  • Protect and evacuate animals.

Latest Flood additions in the Knowledge Base

Thunderstorm over fields in South Africa.
While atmospheric rivers are dreaded for the damage they can cause, they are also essential to the Pacific Northwest and particularly California's water supply, as Qian Cao, a hydrologist at the University of California, San Diego, explains.
Conversation Media Group, the
When disaster hits, vouchers bridge the gap between agricultural livelihood ruin and renewal.
Food and Agriculture Organization of the United Nations - Headquarters
This post examines how different parts of California often see very different water years.
California WaterBlog
Cover and source: Natural Hazards
This research paper assesses two Nature-Based Solutions (NBS) in the Sarantapotamos river basin upstream of Magoula settlement, evaluating their effectiveness through flood hydrograph calculations before and after NBS, and under future climate scenarios.
Cover
The objective of the Rapid Damage and Needs Assessment (RDNA) is to estimate the impact of the storm and floods on physical assets and service delivery in the most affected areas and take stock of the ensuing recovery needs.
An increasing area of interest to researchers is the frequency of compound drought and pluvial flooding (caused by quick, heavy rainfall or sustained rainfall beyond the norm), which is when both occur in succession in the same area.
University of Arkansas
It’s time to recognize the power of healthy forests in managing global growing flood risk, and to shift towards more sustainable forestry practices and policy.
University of British Columbia
A disabled man wading through water logged road on his tricycle in India, 2020
Bihar, once ravaged annually by the relentless floods from the Kosi River, has undergone a remarkable transformation, with the World Bank-supported Bihar Kosi Basin Development project.
World Bank, the

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