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

Data Source

Publishing institution: National Aeronautics and Space Administration (NASA)
The Hazards Mapper home page is a base map of the world with darker shaded areas indicating higher population densities. Custom population estimates generated by the Hazards Mapper are provided by SEDAC’s Population Estimation Service (PES). Population and settlement data are based on SEDAC’s Global Rural-Urban Mapping Project (GRUMP) and Gridded Population of the World, version 3 (GPWv3) data collections. GPWv3 provides a resolution of roughly 4 km (2.5 miles) at the equator. This population resolution will increase significantly when the updated version, GPWv4, is released in 2016. “Our new population layer will be at a resolution of 1 km (0.6 miles) at the equator, which will give higher precision for smaller areas,” says de Sherbinin. Continuously updated data layers that can be overlaid on the base map are available from NASA’s EOSDIS, including data from SEDAC; NASA's Land, Atmosphere Near real-time Capability for EOS (LANCE); and Global Imagery Browse Services (GIBS)...., The default base map includes: Red dots indicating fires and other hotspots detected over the past 48 hours by NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) instrument; Colored circles indicating earthquakes over the past seven days from the USGS Earthquake Hazards Program; Icons indicating the location of individual dams, dam clusters, and nuclear power plants from SEDAC’s Global Reservoir and Dam and Population Exposure Estimates in Proximity to Nuclear Power Plants, Locations databases; and, Colored polygons indicating tornado and flood warnings issued by NOAA (U.S. locations only).
Publishing institution: Wetlands International
Satellite derived rainfall and flooding estimates based on data from NOAA/FEWS.
Publishing institution: United Nations Environment Programme (UNEP)
Satellite based flood maps

Événement

The Asia and Oceania regions are frequently affected by severe natural phenomena such as tropical cyclones, torrential monsoons, volcanic eruptions, yellow sandstorms, floods, sea ice, and wildfires. The importance of monitoring the climate and the environment is also increasing, which has prompted enhanced global interest in the field.

In this area, the new generation of meteorological and earth observation satellites provide frequent and extensive observational information for use in... read more

Actualités

An image of Niamey from a drone. Image: Drone Africa Services.

The government of Niger, in partnership with the World Bank and a team of local volunteers, steps up the gathering of data on Niamey’s exposure to floods using drone and open source data to support disaster preparedness.

The... read more

Publishing date: 26/09/2018

GP-STAR factsheet

Publishing institution: International Centre for Integrated Mountain Development (ICIMOD)

The identification of critical glacial lakes is based on remote sensing method in which several criteria related to glacial lakes, glaciers and physical condition of surrounding area is considered to assess potential for future outburst and possible glacial lake outburst flood (GLOF).

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