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

UN-SPIDER Training Activity

International Training Course on Integration of Multisource Earth Observation Data for Disaster Damage Assessment | Date of training: 25/10/2017 to 31/10/2017
Remote sensing techniques and UN-SPIDER Recommended Practices on droughts and floods | Date of training: 24/07/2017 to 28/07/2017
International Training Course on Space-based Technologies for Flood and Drought Monitoring and Risk Assessment | Date of training: 22/09/2016 to 27/09/2016

Data Source

Publishing institution: VITO
The Proba-Vegetation mission provides information on vegetation, including crop yield and drought, based on PROBA-V and Sentinel-3 data.
Publishing institution: Data Basin
Publishing institution: DMC International Imaging
Very high resolution imagery: 2.5m panchromatic, 5m multispectral 4 spectral bands: Red, Green, Blue, Near-Infrared Imaging modes: stereo, long strip, off-pointing Up to 2000km along track imaging 2 day revisit

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