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

Noticias

Flood inundation map developed using Sentinel-1 satellite data, as part of the rapid mapping response under the SERVIR-HKH Initiative at ICIMOD. Map: Kabir Uddin/ICIMOD.

In July 2019, Bangladesh, India and Nepal experienced floods and landslides during the South Asian... read more

Publishing date: 25/09/2019
Mission team with the director and staff of the Department of Civil Protection and other organizations. Image: DPC.

Upon the request of the Ministry of Territorial Administration (MINAT), Government of Cameroon, UN-SPIDER carried out a week-long Institutional Strengthening Mission (ISM) to Yaoundé from 15 to 19 July. The mission aimed to strengthen the capacities of the Department of Civil Protection (DPC) of Cameroon in using space-based information in all phases of the disaster management cycle. It was the third UN-SPIDER mission to Cameroon after a Technical Advisory Mission (TAM) in 2011 and an Institutional Strengthening Mission (ISM) in 2012, the latter including a training course on “... read more

Publishing date: 22/07/2019
Regional Support Offices mentioned:
Modeled catchment mean annual loss. For clarity, only catchments with a mean annual loss of >$1.5 million have been plotted. Image: Quinn, N., Bates, P. D., Neal, J., Smith, A., Wing, O., Sampson, C., et al. ( 2019).

A recent study, published in the Water Resource Research journal, presents a new method for a spatially realistic national flood risk assessment.

Researchers expanded an existing statistical model, based on U.S. Geological Survey (USGS) river flow data, to simulate a thousand years of potential flood events. By calculating the damage for each event in dollars, they were able to estimate the probability of the United States suffering particular annual flood damages.

Traditional risk flood analysis models assume that the impacts on the entire flood-affected... read more

Publishing date: 04/07/2019

Recommended Practices

Floods and landslides are the first and fourth most frequent disasters around the world (Petley, 2012). There are several examples of downstream flooding caused by massive mudslides where rapid mapping is an indispensable tool for supporting disaster management activities by civil protection authorities. Since July 2014, the Copernicus programme of the European Union has been providing free-of-charge access to Sentinel-1 radar data coveirng the entire world. This allows for the exploration of new applications to strengthen hazard monitoring and disaster mitigation activities. This UN-SPIDER...

UN-SPIDER Training Activity

International Training Programme on Space-Based Technologies for Disaster Risk Assessment | Date of training: 05/09/2019 to 09/09/2019

Evento

The Asia-Pacific region faces major disaster risks in the form of earthquakes and tsunamis, tropical cyclones and typhoons, landslides, flash floods, avalanches and glacial lake outburst floods (GLOFs). Due to the large ... read more

This webinar series will build on the knowledge and skills previously developed in ARSET SAR trainings. Presentations and demonstrations will focus on agriculture and flood applications. Participants will learn to characterize floods with Google Earth Engine. Participants will also learn to analyze synthetic aperture radar (SAR) for agricultural applications, including retrieving soil moisture and identifying crop types.

Learning Objectives: 

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

  1. analyze SAR data in Google Earth Engine
  2. generate soil moisture analyses
  3. identify different types of crops
Course Format: 
  • This webinar series will consist of two, two-hour parts
  • Each part will... read more

Data Source

Publishing institution: Joint Research Center, European Commission (JRC)
GIS Malawi is a webmapper which provides various vector and raster layers covering a broad range of topics including natural hazards.

Advisory Support

Upon the request of the Ministry of Territorial Administration (MINAT), Government of Cameroon, UN-SPIDER carried out a week-long Institutional Strengthening Mission (ISM) to Yaoundé from 15 to 19 July. The mission aimed to strengthen the capacities of the Department of Civil Protection (DPC) of Cameroon in using space-based information in all phases of the disaster management cycle. It was the third UN-SPIDER mission to Cameroon after a Technical Advisory Mission (TAM) in 2011 and an Institutional Strengthening Mission (ISM) in 2012, the latter including a training course on “Remote Sensing for Disaster Management”.

Mission dates: 15/07/2019 to 19/07/2019

As part of the technical advisory support it provides to countries worldwide, UN-SPIDER carried out an Institutional Strengthening Mission to Nepal from 17 to 21 December 2018 upon the request of the government. The mission was a follow-up activity to the Technical Advisory Mission (TAM) to Nepal in July 2017 that assessed use of space-derived information in all aspects of disaster management and offered recommendations and action plan to strengthen the disaster risk management and emergency response in the country. The TAM and ISM were conducted with support from the Ministry of Home Affairs (MoHA). The Nepal GIS Society also offered support in organizing the programme.

Mission dates: 17/12/2018 to 21/12/2018

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