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

News

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 satellite images to identify the maximum spread of the floods, which was observed on 2 May. Waters receded in the following days, although they are still visibile along the border between the two countries on imagery from 12 May.

With the help of Landsat 8 and Sentinel... 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.

The Climate Rainfall Watch website monitors heavy rainfall and drought in near-real-time and collects and stores data from previous months. The website calculates rainfall in percentile: heavy rain is indicated by large percentile value and displayed in dark pink color. The website also monitors drought using the Standardized Precipitation Index (SPI),... read more

Publishing date: 15/04/2020

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...

Event

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 response and recovery
  • Climate change impact
  • Natural flood management
  • Remote sensing in flood applications
  • Water quality
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

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 Remote Sensing Technology. The participation of women in this course is particularly encouraged.

The e-learning course is structured into 3 modules:
-Module 1:... 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 agriculture and food security
  • Acquire specific remote sensing data products that are appropriate for their work
  • Apply remote sensing techniques to crop monitoring,... 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.

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

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