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

News

Image of South Africa acquired on 19 June 2010 by ESA's Envisat satellite. Image: ESA, CC BY-SA 3.0 IGO.

The United Nations Office for Outer Space Affairs, through its UN-SPIDER programme, has activated the International Charter "Space and Major Disasters" on behalf of the National Disaster Management Centre (NDC) of South Africa for the recent floods and mudslides in the country. The German Aerospace Centre (DLR) is acting as project manager for this activation.

Heavy rainfall has been affecting eastern South Africa over the past few days, causing floods and landslides in Durban and the surrounding KwaZulu-Natal province. According to media reports,... read more

Publishing date: 26/04/2019

As part of the technical advisory support it provides to countries worldwide in making use of space-based information for disaster management, UN-SPIDER carries out an Institutional Strengthening Mission to Ecuador from 8 to 12 April 2019 upon the request of the Government of Ecuador. This activity is jointly organized by the United Nations Office for Outer Space Affairs (UNOOSA), through its United Nations Platform for Space-based Information for Disaster Management and Emergency... read more

Publishing date: 08/04/2019

As part of it advisory support activities, UN-SPIDER is carrying out out a Technical Advisory Mission (TAM) to Peru from 1 to 5 April to evaluate the current and potential use of space-based information in all aspects of disaster management. Based on exchanges with a wide range of stakeholders, UN-SPIDER will provide recommendations as to how to strengthen the use of space-based information in disaster risk management and emergency response in the country.

The team of experts led by UN-SPIDER is conducting multiple activities and institutional visits in Lima. The team is comprised of eight experts from UN-SPIDER; the German Aerospace Centre (... read more

Publishing date: 01/04/2019
Parts of Iran (Islamic Republic of) and the region captured by the MODIS instrument on board the Terra satellite on 29 March 2019. Image: NASA Worldview application.

The United Nations Office for Outer Space Affairs (UNOOSA), as part of the support it provides to Member States through its UN-SPIDER programme, has requested the activation of the International Charter "Space and Major Disasters" for monitoring the impact of the floods in the Islamic Republic of Iran caused by heavy rainfall in the southwestern provinces of Golestan and Mazandaran on 31 March. The Charter was activated on behalf of UN-SPIDER Regional Support Office the Iranian Space Agency (ISA), which is acting as project manager for the activation.

A state of emergency has been declared by officials with at least 45 people killed and many more injured as flash flood water and mud damaged thousands of... read more

Publishing date: 31/03/2019
Regional Support Offices mentioned:
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

Event

Course aimed to discover how continental water and ice masses are measured and monitored through... read more

From 22 to 26 July 2019, the training course on Integrated Flood Risk Management (IRFM) will introduce practitioners to the key concepts of IRFM. The course is organized by and held at the Asian Disaster... read more

In the intermediate webinar Remote Sensing for Disasters, participants learn the usage of NASA products to monitor three kinds of disasters. The webinar takes place in three sessions on each Tuesday from 16 until 30 April 2019, starting 10 to 12 am and 2 to 4 pm. It is taught in English and Spanish and is free of charge.

Learning Objectives

By the end of this training, attendees will be able to:

  • Identify NASA data products to characterize and monitor the disasters, Tropical Storms, Flooding, Landslides and Earthquakes, and support decision-making

  • Understand the different data products available and... read more

Advisory Support

As part of the technical advisory support it provides to countries worldwide, UN-SPIDER carried out an Institutional Strengthening Mission to Republic of Ecuador from 8-12 April 2019 upon the request of the government. This activity was jointly organized by the United Nations Office for Outer Space Affairs (UNOOSA), through its United Nations Platform for space-based information for disaster management and emergency response (UN-SPIDER) and the National Risk and Emergency Management Service of Ecuador. The Military Geographic Institute of Ecuador, the Agustín Codazzi Geographic Institute of Colombia (IGAC) and the Federal University of Santa Maria, Rio Grande do Sul, Brazil supported the mission.

Mission dates: 08/04/2019 to 12/04/2019

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