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 Benin

More than 30,000 people are currently homeless in Benin and at least 7,000 hectares of crops are destroyed as a result of flooding. The most affected areas are So-Ava, Cotonou (1st, 2nd,3rd,6th and 9th Arrondissements) and Karimana communes. Indeed, unusually heavy rainfall during this rainy season with more forecasted over the next 3 days, the waters of the rivers Niger and Ouémé experienced unusually rapid rise, overflowing their banks to cause flooding in most parts of the country. The priority area of interest is the south and covers So-Ava Commune, Cotonou and Dangbo Commune.
Source: http://rescommunis.wordpress.com/2010/10/08/disasters-charter-activated-flood-in-benin/
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Floods in Indonesia

Thirteen people were killed and dozens were missing after flash floods smashed through a district in eastern Indonesia's Papua province.

Source: www.glidenumber.net
Flood in Sri Lanka

Te Ministry of Disaster Management reports that over 2000persons affected and 75 house destroyed by pre- monsoon rains.

Source: GLIDEnumber
Flood in Vietnam

HA NOI - Torrential rains brought flooding and landslides to the country's central region, killing at least six people and injuring two.

Source: GLIDEnumber, Vietnam News
Flood in India

At least 63 people have been killed from flooding and landslides in northern India. Authorities have evacuated about 5,000 people to safety from Uttarakhand state.

Source: GLIDEnumber
Flood in Southern Sudan

Floods have displaced nearly 60,000 people in the last month in south Sudan with many at risk of malaria and other diseases.The assessment committee's report states that some 250 families covering 2470 people were affected by the flash floods. It is also reports that 176 families in Panthou have been displaced during the 24 hour torrential downpour that hit part of greater Aweil South County.
Sources: www.alertnet.org, www.reliefweb.int

Status Update: 15/09/2010
Contacts:
UNOOSA/UN-SPIDER
Email: un-spider [at] …
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Flood in The Gambia

On 5 and 6 September 2010 torrential rain recorded 202.6mm which is 20% of total rainfall normally received by the country. The rainfall caused floods almost nationwide affecting over 25,000 people by destroying their residences, and other basic livelihoods. On 7 September 2010, the Government of the Gambia declared a State of National Disaster due to the magnitude and complexity of the floods.

Source: www.glidenumber.net
Flood in Mauritania

Torrential rain from 19 to 21 August 2010 led to the flooding of 8 regions affecting 38 communities. The collapse of houses has led to the displacement of over 1,000 families.

Source: GLIDEnumber
Floods in Senegal

Torrential rain since Thursday, September, 2nd 2010 lead to floods in the main part of Senegal and many towns. The most affected, Dakar, the capital gathers in his suburbs (Pikine and Guediewaye Departements) more than 30,000 affected households. Departement of Velingara in the South of Senegal gathers 1,042 affected people with 105.5 ha of flooded farms.
Source: OCHA- ROWCA
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Status Update: 13/09/2010
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Contacts:
UNOOSA/UN-SPIDER
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Floods in Guatemala

- 44 people have been reported dead, and some 50,364 people have been affected by recent torrential rains.

- The National Coordinator for Disaster Risk Reduction has declared a national level orange alert while the State of National Calamity continues.

- The UN System and the Humanitarian Network have finalized the flash appeal review process In order to continue to support most vulnerable populations.

- UN agencies are currently monitoring the situation on the ground in order to respond and to evaluate the needs of the affected population.

- Food distribution continues in shelters and affected areas around de country.

Source: ReliefWeb

DEADLY landslides in Guatemala are the culmination of one of the worst rainy seasons in half a century, aid workers at Plan International report.

In June, 80,000 people were left homeless…
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