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).

UN-SPIDER Regional Support Offices with hazard-specific expertise

Related content on the Knowledge Portal

  • 697 affected by heavy rains throughout Chile, 4,297 are isolated by the floods.

    Source: Glide number

  • Recent heavy rains in Senegal have caused severe floods in almost all suburbs of Dakar. Dozens of volunteers from the Senegalese Red Cross were dispatched to help disaster victims save their belongings and evacuate their flooded homes. 194 affected families received immediate assistance.

    Source : Glide number

    Heavy rains have caused floods in Dakar and other areas of Senegal. According to officials, a number of deaths were reported so far and houses and roads have been destroyed by floods.
     

    Source: International Charter

    read more
  • Due to Khartoum's heavy rains and flooding, five brothers died following a house collapse in Omdurman, the authorities have confirmed that over 20,000 houses have been destroyed by the rains.

    Source: Glide Number  

    More deaths and destruction of southlands of houses in Khartoum's rain

    Source: Miraya FM

  • VAVUNIYA, 17 August 2009 (IRIN) - Heavy rains exacerbated poor conditions for hundreds of thousands of internally displaced people (IDPs) in northern Sri Lanka over the weekend.

    “We’re not prepared for this. I’m afraid things are going to get much worse,” one international medical officer told IRIN in Vavuniya on 17 August, citing concerns over diarrhoea, dysentery and other waterborne diseases.

    “From an epidemiological point of view, this is a public health disaster waiting to happen.”

    More than 280,000 people live in 30 government camps in Vavuniya, Mannar, Jaffna and Trincomalee districts after fleeing fighting between government forces and the now defeated Liberation Tigers of Tamil Eelam (LTTE) in May.

    Of these, 246,000 are in 14 heavily guarded camps in Vavuniya, mostly in Menik Farm, a sprawling 809ha site divided into six zones about 50km…

    read more
  • ?Heavy rainfall on 16 August caused flash floods originating from the Karamar Mountains in Swabi and Mardan Districts in North West Frontier Province (NWFP), Pakistan. According to various sources, there are reports of 27 deaths, nine people missing, an estimated 400-450 houses destroyed along with massive losses to crops and livestock.

    Source : Glide number

    Ressources from OCHA/Reliefweb, click here

  • On Monday, 10 August 2009, heavy rain occurred in the country made water in the tributary river increased and flooded in 3 districts manly:Sebangfai, Nongbok, and Mahaxay of Khammoune Province. based the first report from provincial disaster management office in Khammoune province, there are 1950 ha of rice areas affected, 1400 meters of irrigation Chanel damage ,600meter of road were cut off, around fishponds damaged.

    Source : Glide number

  • Heavy rain Occurred and Caused flash flood in phongsaly affected 1 District ( Bountai District) around 803 people affected in 10 villagesF, around 218,581 ha affected of rice areas other infrastructure allso affected such as 17 house damaged.

    Source : Glide number

  • Source : Glide number

  • Government alert after rivers over-flowed causing flooding in Región Autónoma del Atlántico Norte, as a result of tropical storms no.17 and 18 - Government providing medical assistance to the households affected, and food to 6821 inhabitants of the area, with the help of the WFP.

    Source : Glide number

    Ressources from OCHA/Reliefweb, click here

    read more
  • At least 10 people were killed in landslides and floods triggered by torrential monsoon rain.

    Source : Glide number

Term Parents

UN-SPIDER Regional Support Offices with hazard-specific expertise