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

Event

Image: Rachman Reilli/Unsplash.

The Global Flood Partnership (GFP) is organizing four webinars as a replacement for the GFP annual in person meeting. These two-hour long webinars (ZOOM meetings/YouTube Streaming) are provided at no cost and take place on 4, 11, 18 and 25 November at 3pm (UTC + 1 hour). Recordings of the webinars can be accessed on YouTube following the events.

The webinars cover the following four topics:

  •  Session 1: Global flood monitoring (EO) - 4 Nov 2020
    • Brian Lander / Margot Van der Velden – WFP, Nobel Peace Prize awardees 2020: 'Taking WFP flood impact prediction and mapping to the next level' YouTube video recording: https://youtu.be/v3NwNcqUs2o
    • David Borges – NASA: 'GEO and CEOS Flood... read more

The University of Alaska Fairbanks has launched a MOOC about Synthetic Aperture Radar (SAR) remote sensing for disaster monitoring. SAR is a remote sensing technology that can see the ground even during darkness and through rain, clouds, or smoke. Participants of the course will gain an intuitive understanding of the information contained in SAR observations and learn to use a range of analysis techniques to apply SAR data to disaster mapping and management. Specific topics will include:

  • The mathematical and physical principles of SAR remote sensing
  • How to access and visualize SAR data
  • Interpretation of SAR images in the context of disaster monitoring
  • Interferometric SAR (InSAR) concepts
  • Flood mapping and SAR change detection for hazard analysis
  • InSAR-based analysis of volcanoes and landslides

The learned concepts will be put into practice in simulated disaster response exercises, in which participants will... read more

Participants at the virtual expert meeting. Image: UNOOSA.

En décadas recientes muchas comunidades en América Latina y el Caribe han experimentado desastres ocasionados por inundaciones, sequías, deslizamientos, terremotos, erupciones volcánicas y maremotos o tsunamis que han erosionado los logros asociados a procesos de desarrollo. Además, en este año 2020 la pandemia ocasionada por el virus COVID-19 ha impactado a muchos países del mundo, forzando a los gobiernos, al sector privado, a la sociedad civil y a organismos regionales e internacionales a modificar sus planes de trabajo. De manera paralela, varios países del Este de África, del Sudoeste de Asia y de América Latina están experimentando los impactos de la plaga de langosta.  

Convencidos que las tecnologías espaciales pueden jugar un papel preponderante en apoyar los esfuerzos que llevan a cabo las instituciones en materia de gestión para la reducción de riesgos, la preparación, la respuesta y la recuperación en caso de desastres; la Asamblea General de las Naciones Unidas... read more

Image: UFSM.

The Federal University of Santa Maria of Brazil (UFSM), in its role as a UN-SPIDER Regional Support Office (RSO), and UN-SPIDER joined forces to conduct a virtual seminar on the use of the UN-SPIDER Recommended Practices to process satellite imagery to map the geographic extent of floods, and to elaborate a series of maps that allow government agencies, as well as regional and international organizations, to assess the severity of droughts in particular years in comparison to droughts in other years. The webinar, conducted on 4 August 2020, brought together more than 30 officers of government agencies of Mozambique, as well as researchers, faculty members and students from various universities.

During the event, researchers from UFSM made participants aware of efforts by the space community to develop drought indices extracted from satellite imagery that assess the impacts of drought on vegetation.  They also gave participants a brief introduction to the use of radar imagery... read more

Regional Support Offices mentioned:

Synthetic Aperture Radar (SAR) data can be acquired day and night, even in cloudy conditions, providing a dense time-series suitable for trend analysis and change detection.  Environmental applications for SAR data include:

  •     forest inventory, biomass estimation and condition monitoring
  •     emergency response to floods and landslides
  •     habitat and crop mapping
  •     soil moisture monitoring
  •     offshore infrastructure and vessel monitoring
  •     detection of pollution such as oil spills and illegal waste

The Joint Nature Conservation Committee (JNCC) is organising a series of online training sessions on understanding, accessing and using SAR data. The training will be delivered by Iain Woodhouse, Professor of Applied Earth Observation at the University of Edinburgh and author of Introduction to Microwave Remote Sensing.

... read more

News

UN-SPIDER and its Regional Support Office in Nigeria, the National Space Research and Development Agency (NASRDA), conducted an online training on the UN-SPIDER Recommended Practice on Flood Mapping and Damage Assessment Using Sentinel-1 SAR Data in Google Earth Engine. Staff from NASRDA as well as from the National Emergency Management Agency (NEMA) of Nigeria participated in the training, which consisted of three two-hour-long online sessions between 21 and 23 October.

The training aimed overall at highlighting the importance and usefulness of remote sensing and satellite data as a decision-making tool in risk and disaster management. In particular, it intended to strengthen the understanding of the characteristics of synthetic aperture radar (SAR) imagery and its use for flood mapping in order to support emergency response efforts in Nigeria,... read more

Publishing date: 24/10/2020
Regional Support Offices mentioned:
Participants at the virtual expert meeting. Image: UNOOSA.

In order to discuss and promote the use of space technologies in addressing natural hazards such as forest fires and landslides in Latin America, UN-SPIDER conducted a virtual regional expert meeting on the topic of “Space-based Solutions for Disaster Risk Reduction and Emergency Response in Latin America” from 22 to 24 September 2020. The meeting was jointly organized with UN-SPIDER Regional Support Offices from Argentina (National Space Activities Commission, CONAE), Brazil (Federal University of Santa Maria, UFSM), Colombia (Geographic Institute Agustin Condazzi, IGAC), and Mexico (Mexican Space Agency, AEM).

In Latin America, UN-SPIDER and its Regional Support Offices have regularly carried out regional expert meetings, training courses and other joint efforts since 2011. The last Regional Expert Meeting took place in 2017 in Mexico.

The meeting, which consisted of three two-hour-long sessions, brought together a total of over 200 disaster management stakeholders... read more

Publishing date: 28/09/2020
A SpaceX Falcon 9 rocket launches the SAOCOM 1B satellite. Image: Manuel Mazzanti/CONAE

The Argentinean SAOCOM 1B satellite was successfully launched into orbit on 30 August 2020. Developed by the National Argentinean Space Commission (CONAE), this new satellite will join SAOCOM 1A and four Italian COSMO-SkyMed to complete the joint Italian-Argentinean Satellite System for Emergency Management (SIASGE). Like its predecessor, SAOCOM 1B was built in Argentina through a joint effort with private companies and universities. It will operate at an elevation of 620 kilometers above the surface of the Earth. A SpaceX Falcon 9 booster launched the satellite from Space Launch Complex 40 at Cape Canaveral Air Force Station in Florida, United States of America.

The SAOCOM 1B satellite has been fitted with a Synthetic Aperture Radar (SAR) sensor that makes use of microwaves in the electromagnetic L-band, which goes through clouds... read more

Publishing date: 14/09/2020
Regional Support Offices mentioned:
Tropical cyclone Fani over the eastern coast of India on 2 May 2019. Image: NASA.

According to the latest issue of an annual disaster statistics report, floods were the deadliest type of disasters in 2019, followed by extreme temperature, while storms affected the highest number of people. Published by the Centre for Research on the Epidemiology of Disasters (CRED), “Natural disasters 2019 - Now is the time to not give up” draws on data recorded in the Emergency Events Database (EM-DAT), which saw the addition of 396 disasters that affected a total of 95 million and caused $103 billion in economic losses around the world. 

Accounting for 40 per cent of disaster events, Asia suffered the highest impact with 45 per cent of deaths and 74 per cent of total affected. India, which saw cyclone Fani cause destruction in 2019, was the country most affected... read more

Publishing date: 20/08/2020
Floods in Bangladesh in 2019. Image: UN Women Asia and the Pacific.

The International Centre for Integrated Mountain Development (ICIMOD) is leveraging space-based information to support government and humanitarian agencies in the Hindu Kush Himalayan (HKH) region with timely information for flood early warning and inundation mapping. The efforts, which consist of developing a streamflow prediction system for flood early warning and of providing near real-time flood maps for disaster response, come as the monsoon floods in the region are worsening and compunding the impacts of the COVID-19 pandemic.

Based at ICIMOD, the streamflow prediction system to support flood early warning is being developed through the SERVIR-HKH initiative, which benefits from technical assistance from NASA and the Bringham Young University. The system provides 15-day streamflow... read more

Publishing date: 19/08/2020

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