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

Actualités

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
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... 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... read more

Publishing date: 03/02/2020

Événement

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

Satellite Remote Sensing for Agricultural Applications logo. Image: NASA

This four-part introductory webinar will focus on data products, data access, and case-studies demonstrating how remote sensing data can be used for decision-making among the agriculture and food security communities.

This training will address how to use remote sensing data for agriculture monitoring, specifically drought and crop monitoring. The webinar will also provide end-users the ability to evaluate which regions of the world agricultural productivity is above or below long-term trends. This informs decisions pertaining to market stability and humanitarian relief.

By the end of this training, attendees will be able to:
  • Identify which satellites and sensors can be used for agricultural applications
  • Understand the limitations of remote sensing and modeled data for... read more

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.

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...

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