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

Update
The U.S. flood insurance market is experiencing a notable transformation, influenced by various factors, from the increasing occurrence of flood events to regulatory developments and advances in modeling.
Moody's Investors Service
Aerial view of flooded houses with dirty water of Dnister River in Halych town, western Ukraine
Update
In Charlotte, North Carolina, flood-prone apartments were converted into a wetland habitat that now helps protect the community from flooding.
Yale Climate Connections
Research briefs
To better predict long-term flooding risk, scientists at the Department of Energy's Oak Ridge National Laboratory developed a 3D modeling framework that captures the complex dynamics of water as it flows across the landscape.
Oak Ridge National Laboratory
View from above of a river going through a jungle forest
Research briefs
Scientists from The University of Manchester, The University of Aberdeen and Newcastle University have found that the restoration of upland peatlands is a highly effective strategy for reducing downstream flooding.
PhysOrg, Omicron Technology Ltd
Update
Billions of francs have since been spent on beefing up flood defences. More money is being poured into solutions, including a CHF1 billion pledge to protect the Rhine Valley between Switzerland and Austria over the next three decades.
swissinfo.ch - International Service of the Swiss Broadcasting Corporation
Update
Scientific assessments reveal that the Third Pole (TP), encompassing the vast glaciated mountain systems of Asia, is warming at an alarming rate of over 0.3 ºC per decade, surpassing the global average.
United Nations Economic and Social Commission for Asia and the Pacific (UN-ESCAP)
Update
Thousands of children in Pakistan are at risk of deadly disease as the country braces itself for above normal monsoon rains and potential flooding that is becoming more frequent and severe due to climate change, said Save the Children.
Save the Children International
Spring flooding along the Ottawa and Bonnechere Rivers, Ottawa Valley, Ontario Canada
Research briefs
This week, large areas of Ontario experienced severe flooding that caused widespread power outages, water damages and disruption. Severe rainfall events are not new, but they are becoming more frequent and costly due to human-caused climate change.
Conversation Media Group, the
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