Flood

Definition

Flood is usually used as a general term to describe the overflow of water from a stream channel into normally dry land in the floodplain (riverine flooding), higher-than–normal levels along the coast and in lakes or reservoirs (coastal flooding) as well as ponding of water at or near the point where the rain fell (flash floods) (IRDR Glossary).

Facts and figures

Floods are the natural hazard with the highest frequency and the widest geographical distribution worldwide. According to the Organization for Economic Cooperation and Development (OECD)  flooding is one of the most common, widespread and destructive natural perils, affecting approximately 250 million people worldwide and causing more than $40 billion in damage and losses on an annual basis (OECD).

Flooding occurs most commonly from heavy rainfall when natural watercourses lack the capacity to convey excess water. It can also result from other phenomena, particularly in coastal areas, by a storm surge associated with a tropical cyclone, a tsunami or a high tide. Dam failure, triggered by an earthquake, for instance, will lead to flooding of the downstream area, even in dry weather conditions.

Various climatic and non-climatic processes can result in different types of floods: riverine floods, flash floods, urban floods, glacial lake outburst floods and coastal floods.

Flood magnitude depends on precipitation intensity, volume, timing and phase, from the antecedent conditions of rivers and the drainage basins (frozen or not or saturated soil moisture or unsaturated) and status. Climatological parameters that are likely to be affected by climate change are precipitation, windstorms, storm surges and sea-level rise (UNDRR).

When floodwaters recede, affected areas are often blanketed in silt and mud. The water and landscape can be contaminated with hazardous materials such as sharp debris, pesticides, fuel, and untreated sewage. Potentially dangerous mold blooms can quickly overwhelm water-soaked structures. Residents of flooded areas can be left without power and clean drinking water, leading to outbreaks of deadly waterborne diseases like typhoid, hepatitis A, and cholera (UNDRR).

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Related content on the Knowledge Portal

  • At least 23 people were killed when floods swept the Turkish city of Istanbul, swamping houses, turning highways into fast-flowing rivers and drowning seven women in a minibus that was taking them to work.

    Source: Glide number

     

    Heavy rains over the Marmara Region affected the districts of Silivri, Catalca, B. Cekmece, K. Cekmece and Bakirkoy in Istanbul. By the afternoon of 9 September, 31 casualties were reported, along with missing people.

    Source: International Charter

     

     

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  • Due to the rainy season and recent floods, Liberia has experienced significant flooding near Monrovia. Together with other West and Central African countries, over 200,000 were affected.

    Source: Glide number

  • Due to the rainy season and recent floods, Sierra Leone has experienced significant flooding. 15 people were died and 425 displaced in Freetown, 6 villages in the Kambia District lost all their crops.

    Source: Glide number

  • Due to the rainy season and recent floods, Guinea has experienced significant flooding together with other West and Central African countries. Over 1,000 were affected and IFRC mobilized relief operation for the targeted 500 families. 
     
    Sorce: Glide number

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  • Mali have been affected by heavy rains and wind storm which had a serious impact. 80 families have been affected.

    Source: Glide number

  • Gambia have been affected by heavy rains. GRCS reported on 3 Septemberthet 48 households are homeless.

    Source: Glide number

  • Intense rains in northern Air Mountains and desert towns affected 7,000 households, damaged 3,500 homes in the commune of Agadez.

    Source: Glide number

  • At least three people died and thousands were homeless Tuesday(01/09/2009) in Ouagadougou and its suburbs as the capital of Burkina Faso was hit by floods, officials said - AFP 02/09/2009.

    Source: Glide number

    Heavy rainfall caused severe flooding in the capital of Burkina Faso, Ouagadougou since 1 September 2009. Roads, bridges and dams have been badly damaged, and a main hospital in the capital is flooded. According to officials, 5 deaths were reported so far and more that 150,000 people left homeless.

    Source: International Charter

     

    read more
  • Heavy rains caused flooding in Jalabad, eastern Afghanistan. 626 houses destroyed, roughly 4000 people affected. (UNAMA Press Release 01/09/2009)

    Source: Glide number

  • A child was killed and more than 3,500 people were left homeless when heavy rains caused houses to collapse in southwestern Mauritania, state media reported on Saturday (29/08/2009)

    Source: Glide number

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