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).

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Advisory Support

At the request of, and in coordination with the National Civil Protection Office of Tunisia, UN-SPIDER is conducting a Technical Advisory Mission to Tunisia from 4 to 6 March 2020 to identify the needs of the country to fully take advantage of space-based information for disaster management. In order to discuss the use of space-based information for risk and disaster management to subsequently make recommendations on improvements, the expert team meets with key disaster management authorities in the country.

The mission is conducted with the support of experts from the Algerian Space Agency (ASAL); the Romanian Space Agency (ROSA); the United Nations Economic Commission for Africa (UNECA); the National Observatory of Athens (NOA); and an expert on the Copernicus Emergency Management Service. The mission team is also benefiting from the support of the Chief of Space Applications of the United Nations Office for Outer Space Affairs.

As part of the mission, the team of experts will visit several institutions including the National Office of Civil Protection; the Directorate General for Forests of the Ministry of Agriculture; the Faculty of Sciences of Tunis, University of Tunis El Manar; the National Agronomic Institute of Tunisia; the National Institute of Meteorology; as well as at the Ministry of Local Affairs and Environment. Meetings will also be conducted with representatives of the National Cartographic and Remote Sensing Centre of Tunisia and other organizations. In addition, the TAM team will meet the United Nations Country Team in Tunisia, which supports disaster management efforts in the country.

During the TAM, a workshop with over 20 participants from nine institutions will take place in order to present the UN-SPIDER programme to Tunisian counterparts involved in disaster management, and encourage inter-institutional cooperation and sharing of geospatial information among them.

UN-SPIDER aims at ensuring all countries have the capacity to use all types of space-based information to support risk and disaster management efforts. To make sure that all interested stakeholders can benefit from this information in the most effective way possible, UN-SPIDER provides Technical Advisory Support to Member States through missions such as this one.

The Algerian Space Agency (ASAL), the Romanian Space Agency (ROSA) and the National Observatory of Athens (NOA) are UN-SPIDER Regional Support Office.

On request of the Tunisian Government and immediately after the technical advisory mission, UN-SPIDER conducted a three-day hands-on training on the use of Sentinel-1 radar data for flood mapping. In order to further strengthen the capacity of Tunisia to use space technologies for disaster management, UN-SPIDER will continue to encourage the participation of Tunisian institutions in its conferences and expert meetings. In addition, together with its regional and international partners, UN-SPIDER will provide training on forest fire mapping in the medium term. 

Mission dates: 04/03/2020 to 06/03/2020

UN-SPIDER Training Activity

Flood mapping with Sentinel-1 radar data | Date of training: 09/03/2020 to 11/03/2020

Data Source

Publishing institution: The University of Tokyo
MERIT Hydro is a global hydrography datasets, developed based on the MERIT DEM and multiple inland water maps. It contains flow direction, flow accumulation, hydrologically adjusted elevations, and river channel width., High-resolution raster hydrography maps are a fundamental data source for many geoscience applications. Here we introduce MERIT Hydro, a new global flow direction map at 3 arc-second resolution (~90 m at the equator) derived from the latest elevation data (MERIT DEM) and water body datasets (G1WBM, GSWO, and OpenStreetMap). We developed a new algorithm to extract river networks near-automatically by separating actual inland basins from dummy depressions caused by the errors in input elevation data. After a minimum amount of hand-editing, the constructed hydrography map shows good agreement with existing quality-controlled river network datasets in terms of flow accumulation area and river basin shape. The location of river streamlines was realistically aligned with existing satellite-based global river channel data. Relative error in the drainage area was smaller than 0.05 for 90% of GRDC gauges, confirming the accuracy of the delineated global river networks. Discrepancies in flow...
Publishing institution: Airbus Defence & Space
OneAtlas is a collaborative environment to easily access very high resolution imagery, perform large-scale image processing, extract industry specific insights and benefit from Airbus assets to develop solutions. The services include infrastructure change detection, vehicle detection & counting and will soon cover aircraft detection and land use change detection as well . Airbus provides the services through a buy-what-you-need option. It is possible to test the functionalities with a 30-days Free Trial.
Publishing institution: Geoscience Australia
The Digital Earth Africa (DE Africa) Map is a website for map-based access to spatial information. It’s is still being developed by Data61 CSIRO in collaboration with Geoscience Australia. DE Africa is leveraging international Earth Observation (EO) data and science to produce new information and services that benefit African countries. Through translating data into ready-to-use insights, more informed decisions about soil and coastal erosion, agriculture, deforestation, desertification, water quality and changes to human settlements can be made. The data is organized in data-cubes and will be fully available by 2020.

Noticias

Participants during the training on flood mapping using SNAP and QGIS.

To support the National Office of Civil Protection (ONPC) of Tunisia and other government agencies in using space-based information for disaster management, UN-SPIDER conducted a three-day training in Tunis from 9 to 11 March. The course highlighted the relevance and usefulness of remote sensing and satellite data as a decision-making tool in risk and disaster management. It focused on the UN-SPIDER Recommended Practice for flood mapping with Sentinel-1 radar data to support authorities in responding to recurring floods in the country.

Twelve participants attended the event, which introduced them to remote sensing and provided an overview of synthetic-aperture radar (SAR) principles, before walking them step-by-step through downloading, processing and mapping data from the Sentinel-1 satellite using the free and open source software solutions SNAP and QGIS. The training also... read more

Publishing date: 10/03/2020
The terminus of Bear Glacier occurs in iceberg filled freshwater lagoon. Kenai Fjords National Park, Alaska. Image: NASA.

Scientists from 50 scientific institutions, led by the National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA) combined 26 independent satellite datasets to show that the Greenland Ice Sheet melt is increasing. The group studied data from 1992 to 2018, taking direct measurements of the continent-sized glacier. The study found that decade averages for ice melt has increased sevenfold from the 1990s. 

The report shows that 1992 to 2002 averaged 1mm/decade in melt, 2008 to 2018 increased to a 7mm/decade loss. The research pulled from USGS’s Landsat mission, the oldest open-access Earth observation data. The total was also calculated using space-based gravity measurements - which measures total mass on the world’s largest island - integrated with remotely sensed height measurements and water flow models to create an Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE) for a complete understanding of the total ice found on... read more

Publishing date: 03/02/2020
Image: UNOOSA.

In order for South Asian Association for Regional Cooperation (SAARC) Member States to be able to incorporate the routine use of space technology-based solutions, there is a need to increase awareness, build national capacity and develop solutions that are customized to their needs. The regional workshop and capacity-building programme on the "Role of Earth Observation in Multi-Hazard Disaster Risk Assessment and Monitoring Targets of the Sendai Framework" is the second regional event in South Asia under the umbrella of the SAARC Disaster Management Center and the United Nations Office for Outer Space Affairs (UNOOSA), through its UN-SPIDER programme. The event took place in collaboration with the International Water Management Institute (IWMI), Sri Lanka, the Space Applications Centre of the Indian Space Research Organisation (ISRO) and the Centre for Space Science and Technology Education in Asia Pacific (CSSTEAP). It was built on the outcome of the first regional workshop and... read more

Publishing date: 12/12/2019
Regional Support Offices mentioned:

Recommended Practices

SAR-based flood mapping is a standard and reliable method for determining the extent of major floods. SAR can penetrate cloud-cover, operate in any weather conditions and provide timely and crucial information about one of the most frequent and devastating natural disasters: flooding. Too often limited technical know-how separates the disaster community from the information they need; this Recommended Practice provides a near real-time, cloud-based and easy-to-use method for flood extent mapping, designed to overcome technical limitations. Without the need for downloading large and complex...
Flood hazard assessments are critical to identifying areas at risk and taking relevant preparation and mitigation measures to address the hazard. Using the HEC-RAS 2D model for preparing flood hazard maps, this Recommended Practice explains how to identify flood-prone areas and exposed infrastructure. Through its focus on the prevention and mitigation stages of the disaster management cycle, it complements the Recommended Practice on Flood Mapping and Damage Assessment with Sentinel-2, also developed by SUPARCO.
Regional Support Offices mentioned:

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