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).

Related content on the Knowledge Portal

GP-STAR factsheet

Dissemination of automatically derived flood information via a web-client (light blue: flood area; dark blue: permanent water surface). The example shows a flood situation in the eastern part of India on September 04, 2016, observed by Sentinel-1 data.
Publishing institution: German Aerospace Center (DLR)

The automatically derived flood masks are based on Sentinel-1 and TerraSAR-X radar data. TerraSAR-X data can be accessed free of cost via scientific data proposals or are provided by DLR during activations of the International Charter ‘Space and Major Disasters’. Data from Sentinel-1 is accessible free of cost via ESA’s Copernicus Open Access Hub.

Publishing institution: German Aerospace Center (DLR)

For a comprehensive and objective analysis of the settlement patterns, the DLR additionally developed an approach to display the spatial networks between the mapped settlements. It enables the computation of various form and centrality measures to characterize settlement patterns, at different spatial units, ranging from global to local scale.

Publishing institution: Copernicus Emergency Management Service (Copernicus EMS)

CEMS is a core service of the European Union’s Earth Observation programme Copernicus. It supports all phases of the disaster management cycle by delivering warnings and risk assessments of floods and forest fires and by providing geospatial information derived from satellite images on the impact of natural and man-made disasters all over the world (before, during or after a crisis). The two Mapping services of CEMS (Rapid Mapping, Risk and Recovery Mapping) are delivering products since April 2012. The Risk & Recovery Mapping provided for example information for preparedness, disaster risk assessment and risk reduction related to earthquakes in Nepal, several post-disaster assessments for flood and fire events, reconstruction and recovery monitoring in Haiti, and multi-risk assessments for the Azores Islands in Portugal. 

CEMS is coordinated by the European Commission (joint coordination between the Directorate Generals ECHO, JRC, GROW). Activation requests are... read more

Recommended Practices

As a means of emergency response after a flooding event or inland inundation, flood mapping helps to estimate the extent of the flood on a large scale. It is a basis of coordinating appropriate recovery activities, rehabilitation and prevention measures for possible upcoming events. This UN-SPIDER Recommended Practice on flood mapping and damage assessment explains the use of Sentinel-2 (S2) optical satellite data from the European Space Agency (ESA), which acquires data in 13 spectral bands. It provides hands-on practice to calculate the Normalized Difference Water Index (NDWI) to determine...
Regional Support Offices mentioned:

Noticias

Logo of the International Charter "Space and Major Disasters"

The International Charter “Space and Major Disasters” has been activated for floods in Venezuela on 15 August and in India on 16 August.

Floods in Venezuela

In Venezuela, persistent heavy rain and swollen rivers have caused severe flooding, which has affected over 10,000 people in the Venezuelan provinces of Amazonas, Apure, Bolivar and Anzoategui. The Orinoco river reached its highest levels in 40 years, leading the river to burst its banks in my places. Local authorities have set up an aerial bridge over the river so supplies of food, medicine and aid can reach the affected populations. Major arterial roads have also been closed, isolating some areas and further hampering emergency response efforts.

The red alert for rain and flooding is set to be in place until the end of August, with further rain forecast in the coming weeks.

The Charter activation was made by Venezuelan civil protection agency “... read more

Publishing date: 16/08/2018

The United Nations Office for Outer Space Affairs (UNOOSA) and the United Nations Institute for Training and Research (UNITAR) Operational Satellite Applications Programme (UNOSAT) have jointly activated the International Charter “Space and Major Disasters” for the recent floods in Lao People’s Democratic Republic on 24 July 2018. UNOOSA activated the Charter on behalf of the country’s Ministry of Science and Technology and Department of Disaster Management and Climate, while UNITAR-UNOSAT activated the emergency mechanism on behalf of the World Food Program (WFP).

At least 20 people have been killed and hundreds of people remain missing after floods struck the country's Attapeu province. The collapse of the Xe-Pian Xe-Namnoy hydroelectric dam released 5 billion cubic meters of water downstream, flooding at least 7 villages and washing away homes.

Emergency responders are now working to rescue people from the area, evacuate them to emergency shelters and search for... read more

Publishing date: 27/07/2018
Global Precipitation Measurement visualization of heavy rain in Japan, 2 – 9 July 2018. Image: NASA Earth Observatory

The International Charter “Space and Major Disasters” was activated on 7 July for a major flooding disaster which has hit Japan, the worst the country has experienced in 36 years.

Heavy rains, which first started at the end of June 2018, caused flash flooding and deadly landslides across western and central Japan from 5 July. Over 200 fatalities have been recorded in the country so far as a result of the disaster. The rains which caused the flooding appear to have been caused by warm, humid air flowing from the Pacific Ocean and by remnants of Typhoon Prapiroon, both of which intensified the seasonal rain front. Some 8.63 million people across 23 prefectures in Japan have been... read more

Publishing date: 16/07/2018
Flooding in India (2013). Photo: Umesh Kumar.

India’s Central Water Commission (CWC) has signed a Collaboration Agreement with Google that will help crisis management agencies deal with extreme hydrological events, such as floods, more effectively. 

The agreement allows CWC to make use of Google’s artificial intelligence, machine learning and geospatial mapping expertise for effective water management and flood forecasting. The agreement will also help CWC to better disseminate flood related information through different platforms developed by Google. 

Under this Agreement, CWC and Google will share technical expertise in different fields related to flood management, including  geospatial flood mapping and analysis of hydrological observation data. The agreement also facilitates collaboration on improving flood prediction systems, which will help provide location-targeted, actionable flood warnings; a high priority research project utilizing Google Earth Engine to help visualize and improve... read more

Publishing date: 10/07/2018
Logo of the International Charter "Space and Major Disasters"

The International Charter Space and Major Disasters has been activated for flooding in Yemen on 2 June.

Cyclone Mekunu brought severe rainfall and winds causing flooding in areas of Yemen as it made landfall on 25 May. Local reports suggest that at least seven people have been killed and over 1,000 families have been displaced due to the flooding. The cyclone and floods have also damaged infrastructure and agricultural equipment in many districts of the Yemeni mainland. Some 120 fishing ships have reportedly been lost to the cyclone and a search is ongoing for missing fishermen.

One of the worst affected areas is the Yemeni island of Socotra in the Arabian Sea. Residents on the island are fleeing from torrential floods and more than 30 people are reported missing. Smaller islands off the coast of Socotra have also been heavily impacted and there is growing concern for the 2,500 families living on the islands of Abd Al Quri and Samhah as... read more

Publishing date: 04/06/2018

Data Source

Publishing institution: European Space Agency (ESA)
The main objective of the SENTINEL-3 mission is to monitor sea and land surface temperature, sea surface topography and ocean and land surface colour with high accuracy and reliability. The high resolution data is meant to support ocean forecasting systems, environmental monitoring and climate monitoring. ESA and EUMETSAT will jointly operate the SENTINEL-3 mission and bothy institutions provide access to the processed data. Sentinel 3 carries four main instruments: the OLCI, SLSTR, Altimetry and a MWR Microwave Radiometer.

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