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).

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Actualités

This image captured by the Copernicus Sentinel-2A satellite on 28 December 2015. It demonstrates Nepal’s varied terrain from the mountains to the north (left side) to the plains in the south (right side). Vegetation appears red in this false-colour image, while waterways and buildings appear light green and blue. Image: ESA.

On 12 March, Nepal Telecommunications Authority (NTA) signed an agreement with French satellite operator Thales Alenia Space to build Nepal’s first communications satellite. The Nepalese government intends to use the satellite to provide nationwide internet access to its citizens, improve disaster management efforts and strengthen economic growth in the country.

The development of Nepal’s own satellite system proves to be significant in terms of improving the country’s disaster management efforts. Nepal... read more

Publishing date: 29/03/2019
Participants during national training programme in Lao People's Democratic Republic.

As part of the technical advisory support it provides to countries worldwide on accessing space-based information for disaster management and emergency response, UN-SPIDER carried out an Institutional Strengthening Mission to Lao People’s Democratic Republic from 18 to 22 March 2019 upon the request of the Ministry of Science and... read more

Publishing date: 20/03/2019
Participants are being trained in analyzing maps produced as part of International Charter activations.

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Publishing date: 19/03/2019
Landsat 8 captured the Lower Sesan II Dam and its adjacent rivers on 1 February 2018. While in 2010, 3 percent of Cambodia’s domestically generated electricity came from hydropower, by 2016, hydropower supplied 60 percent. Image: NASA.

Vietnamese and American researchers joined efforts to develop a satellite-based system approach to monitor and manage transboundary flooding.

The teams from the Viet Nam National Center for Water Resources Planning and Investigation (NAWAPI) and the University of Washington co-developed and implemented an advanced water forecasting system. Recently, Viet Nam launched the satellite-based system aiming to improve timely access to upstream reservoir information in transboundary river basins of the Red and Mekong rivers. The satellite-based system provides various ways to achieve this objective.

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Publishing date: 06/03/2019
Image of the tailings dam flood on 30 January acquired by Operational Land Imager (OLI) on Landsat 8. Image: NASA.

The International Charter “Space and Major Disasters” has been activated for floods in Brazil following the collapse of a mining dam. The activation was requested by the Brazilian Disaster and Risk Management National Centre (CENAD). The country’s Ministry of Regional Development is acting as project manager for the activation.

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Publishing date: 25/01/2019
Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite captured false-color images of the State of Rio Grande Du Sul  in 2007 Image: NASA

The International Charter “Space and Major Disasters” has been activated for floods in Brazil by the Brazilian Disaster and Risk Management National Centre (CENAD). The country’s Ministry of National Integration is acting as project manager for the activation.

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Publishing date: 14/01/2019

Data Source

Screenshot of Zansea
Publishing institution: Tanzania Commission for Science and Technology (COSTECH)
The Tanzania Commission for Science and Technology (COSTECH), in partnership with the Revolutionary Government of Zanzibar (RGoZ), has launched an initiative to produce detailed aerial imagery maps of the islands of Zanzibar. The cooperative project is called the Zanzibar Mapping Initiative (ZMI). This initiative has drawn global attention because the mapping is done entirely with drones; the ability to map is now available widespread at a local level. The maps produced are of exceptional spatial resolution. Additionally, their free and open source data sets includes a comprehensive compilation of available vector and raster data covering the whole of Tanzania. Users can find not only aerial imagery produced from drones, but everything from census data to land use layers. More information can be found on the ZMI project website: http://www.zanzibarmapping.com/
Publishing institution: The University of Tokyo
The MERIT DEM was developed by removing multiple error components (absolute bias, stripe noise, speckle noise, and tree height bias) from the existing spaceborne DEMs (SRTM3 v2.1 and AW3D-30m v1). It represents the terrain elevations at a 3sec resolution (~90m at the equator), and covers land areas between 90N-60S, referenced to EGM96 geoid.
Screenshot of FLOPROS: an evolving global database of flood protection standards
Publishing institution: Vrije Universiteit Amsterdam and Deltares
Assessments of flood risk, on global to local scales, are becoming more urgent with ongoing climate change and with rapid socioeconomic developments. Such assessments need information about existing flood protection, still largely unavailable. Here we present the first open-source database of FLood PROtection Standards, FLOPROS, which enables more accurate modelling of flood risk. We also invite specialists to contribute new information to this evolving database.

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