Flood

This Copernicus Sentinel-1 image combines two acquisitions over the same area of eastern Iraq, one from 14 November 2018 before heavy rains fell and one from 26 November 2018 after the storms. The image reveals the extent of flash flooding in red, near the town of Kut. Image: modified Copernicus Sentinel data (2018), processed by ESA, CC BY-SA 3.0 IGO.

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).

Further information

UN Guidelines for Reducing Flood Losses

OECD Report on Financial Management of Flood Risk

PreventionWeb Floods

UN-SPIDER Regional Support Offices with hazard-specific expertise

Title: Argentina Regional Support Office

Title: Asian Disaster Reduction Center (ADRC)

Title: Brazil Regional Support Office

Title: ERATOSTHENES Centre of Excellence

Title: Germany Regional Support Office

Title: Greece Regional Support Office

Title: Indonesia Regional Support Office

Title: International Centre for Integrated Mountain Development (ICIMOD)

Title: International Water Management Institute (IWMI)

Title: Nigeria Regional Support Office

Title: Pakistan Regional Support Office

Title: Romania Regional Support Office

Title: South Africa Regional Support Office

Title: United States of America Regional Support Office

Related content on the Knowledge Portal

Floods in Iraq

In the Erbil and Dahuk Governorates over 3,000 persons (500 families) across ten locations in the mountainous districts of Mergasur, Rawanduz, Choman, Zhakho, Sumel, Aqra were affected by flash flooding following heavy rains and winds on 1 Nov 2009.

Source: http://www.glidenumber.net/glide/public/search/details.jsp?glide=18963.
Floods in Colombia

529 people affected by floods in municipality of Guapi, Cauca.

Source: http://www.glidenumber.net/glide/public/search/details.jsp?glide=18961.
Floods in Panama

At least 186 people have been affected by heavy rains in Los Santos Province since late October.

Source: http://www.glidenumber.net/glide/public/search/details.jsp?glide=18960.
Floods in Brazil

Heavy rains have affected more than 680,000 people in Espirito Santo, southeastern Brazil. 4,500 people have been evacuated and 112,300 houses have suffered damages.

Source: http://www.glidenumber.net/glide/public/search/details.jsp?glide=18959.
Floods in El Salvador

Floods due to heavy rain have killed 91 in the departments of Salvador, La Libertad, Cuscatlán, La Paz, San Vicente.
Source: http://www.glidenumber.net/glide/public/search/details.jsp?glide=18958.

Available Space-based Information for: El Salvador - Floods and Landslides - 09 Nov 2009
Status Updated 15/11/2009

UNOOSA/UN-SPIDER:
Email: un-spider [at] unoosa.org
Link: http://www.un-spider.org/

ReliefWeb:
Available maps for Hurricane Ida
Link:…
read more
Flood in Thailand

Floods caused by heavy rains have claimed 15 lives in Thailand's southernmost provinces of Songkhla, Narathiwat, Pattani and Yala.

http://www.glidenumber.net/glide/public/search/details.jsp?glide=18957.
Floods in Paraguay

Hundreds of families have been affected by floods in Encarnacion (Itapua), Ayolas (Misiones), Ciudad del Este (Alto Parana) e Ita Cora (Neembucu).

Source: http://www.glidenumber.net/glide/public/search/details.jsp?glide=18939&record=1&last=4495

Information on Reliefweb: http://www.reliefweb.int/rw/dbc.nsf/doc108?OpenForm&emid=FL-2009-000226-PRY
Floods in Chad

On 12 and 14 September 2009, two heavy torrential rains poured down in the capital N?Djamena leading to the flooding of almost half of the town. The stormy rains aggravated the already worse situation that started since the beginning of the rainy season. The most affected areas are Walia, Kamda, Toukra, Habena, Chagoua, and Moursal.The Red Cross of Chad?s urban committee conducted a rapid assessment and estimated that over 545 houses were destroyed.

Source: http://glidenumber.net/glide/public/search/details.jsp?glide=18925.
Floods in Nepal

Unseasonably heavy rains in western Nepal left a trail of destruction Tuesday(05/10/2009), killing at least 36 people and injuring several others, official said. Government officials said landslides struck at least five districts in western Nepal while flash floods were reported in Nepal's plains, known as Terai, after heavy rain began falling Sunday evening.

Source:http://glidenumber.net/glide/public/search/details.jsp?glide=18924.
Floods in Kenya

On 21 September 2009, three people died and property was destroyed during floods that occurred in Kisumu and Nyando districts, Nyanza province. Floods in the Kisumu district occurred in Winam and Kadibo divisions, killing three (3) people and affecting about 10,000 people. Floods in the flood prone district of Nyando occurred in Miwani division. 1126 people (206 households) had their houses submerged and an additional 3,000 people were affected by the floods.

Source: http://www.glidenumber.net/glide/public/search/details.jsp?glide=18923&record=1&last=4.

read more