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

Advisory Support

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 Technology. This activity was jointly organized by the United Nations platform for Space-based Information for Disaster Management and Emergency Response (UN-SPIDER) of the United Nations Office for Outer Space Affairs (UNOOSA) and the Ministry of Science and Technology (MOST).

Mission dates: 18/03/2019 to 22/03/2019

As part of the technical advisory support it provides to countries worldwide, UN-SPIDER carried out an Institutional Strengthening Mission to Myanmar from 11 to 15 March 2019 upon the request of the government. This activity was jointly organized by UN-SPIDER and the United Nations Human Settlement Programme (UN-Habitat), under auspices of the Ministry of Social Welfare, Relief and Resettle­ment (MSWRR) of Myanmar. It was hosted by the Emergency Operation Centre (EOC). 

Mission dates: 11/03/2019 to 15/03/2019

News

Satellite image over the eastern part of the Sundarbans in Bangladesh. Image: European Space Agency.

To support emergency response efforts, the International Centre for Integrated Mountain Development (ICIMOD) has mapped the extent of floods in Bangladesh following... read more

Publishing date: 09/06/2020
Sentinel-2 imagery of the area on 4 May. Image: CSSTEAP.

Using space-based information, the Centre for Space Science and Technology Education in Asia and the Pacific (CSSTEAP) affiliated to the United Nations has analysed the recent failure of a dam around the Sardoba Reservoir in Uzbekistan. Following a week of heavy rain in the region, the wall of the dam broke on 1 May and flooded surroundings in Uzbekistan as well as Kazakhstan to the north. According to media reports, the breach led to the evacuation of thousands of people in the area. 

The analysis carried out by CSSTEAP makes use of MODIS multi-temporal... read more

Publishing date: 19/05/2020
JAXA Climate Rainfall Watch. Image: JAXA.

The Japan Aerospace Exploration Agency (JAXA) has released the JAXA Climate Rainfall Watch website to monitor extreme weather and climate over the world. The website provides hourly global measurements of precipitation as well as forecasts about heavy rainfall and drought in different temporal scales (daily, pentad, weekly, 10-days and monthly). The satellite-based global rainfall maps produce highly accurate measurements that can help better understand the changing climate, improve forecasts of extreme weather events, such as floods and droughts, minimize their damage and strengthen early warning systems.... read more

Publishing date: 15/04/2020

Event

Grace webinar. Image: NASA
This... read more
7th International Conference on Flood and Urban Water Management logo. Image: WIT

The meeting aims to attract researchers, academics and practitioners actively involved in improving our understanding of urban water systems and flood events.

FRIAR 2020 will generate an improved understanding of emerging flood risk management and urban water management challenges, drawing on the expertise of numerous disciplines and considering a range of responses. The conference provides a rich forum for the development of innovative solutions that can help bring about multiple benefits toward achieving integrated flood risk and urban water management strategies and policy.

The topics include:

  • Flood risk management
  • Flood warning and forecasting
  • Flood ... read more
Introduction to Geospatial Information Technology Applications, Flood Forecasting and Early Warning Systems in West Africa logo. Image: UNITAR

The aim of these e-courses is to introduce the basic concepts of flood forecasting practices and Early Warning Systems in ECOWAS region. Participants will go through selected case studies of operational Early Warning Systems services and Geospatial Information Technology applications for Disaster Risk Reduction relevant to support operational decision making for enhanced flood management in ECOWAS region. 

The course is designed to accommodate participants from a variety of backgrounds and early career technical staff from governmental institutions of ECOWAS member states working in disaster risk management sector and hydro-meteorological services. Registered participants should have an academic background and/or professional knowledge... read more

Introduction to Geospatial Information Technology Applications, Flood Forecasting and Early Warning Systems in West Africa logo. Image: UNITAR

The aim of these e-courses is to introduce the basic concepts of flood forecasting practices and Early Warning Systems in ECOWAS region. Participants will go through selected case studies of operational Early Warning Systems services and Geospatial Information Technology applications for Disaster Risk Reduction relevant to support operational decision making for enhanced flood management in ECOWAS region. 

The course is designed to accommodate participants from a variety of backgrounds and early career technical staff from governmental institutions of ECOWAS member states working in disaster risk management sector and hydro-meteorological services. Registered participants should have an academic background and/or professional knowledge of hydromet numerical applications and basic knowledge in GIS and... read more

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