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

Cover
Using a high-resolution dataset of 8.2 million households in Bangladesh’s coastal zone, researchers assess the extent to which infrastructure service disruptions induced by disasters can thwart progress towards the Sustainable Development Goals.
In October 2023, County Cork was struck by two days of extreme rainfall from Storm Babet that fell on already saturated soils. Swollen rivers led to severe flooding in Midleton.
World Weather Attribution
Women's empowerment programme in Jordan
Today is World Civil Defense Day, honouring the dedication and efforts of civil defense organizations and their partners in protecting people, homes and businesses from disasters and emergencies.
Flood Resilience Portal
Landslide on the way from Hapao village in Banaue province in the Philippines, affecting the road taken by a bus
Researchers from several countries collaborated to assess to what extent human-induced climate change altered the likelihood and intensity of the weather conditions at the time of the most impactful floods in Mindanao Island.
World Weather Attribution
Cover
This study informs NYC’s residents of their current and future flood risk and enables the development of tailored solutions to manage increasing flood risk in the city.
Cover and source: Natural Hazards (Springer)
This study finds that the average number of fatalities per flood event has declined over time. Mortality fractions per event have decreased over time for middle- and high-middle-income countries, but increased for low-income countries.
Cover and source: International Journal of Disaster Risk Science
This study aimed to examine the vulnerability of flood-prone rural communities in southern Punjab, Pakistan to external shocks by analyzing data from 365 communities.
The Pearl River has been identified as one of the world’s most vulnerable regions to flood exposure. Model simulations even suggest that future surface warming can enhance both the intensity and frequency of extreme rainfall in this region.
SciTechDaily

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