# Flood risk mapping and early warning with satellite data Satellites help before and during a flood. Before, archived flood extents and maps of sealed ground can add to the flood hazard and risk maps that EU member states must keep. During an event, radar satellites map the water through cloud, day and night, and the European Flood Awareness System gives authorities flood forecasts up to ten days ahead. ## How it works Satellite data supports three tasks that use different services: mapping the risk before a flood, forecasting a flood, and mapping the water while it is there. ### Risk maps before a flood EU member states keep flood hazard and flood risk maps for scenarios of low, medium and, where appropriate, high probability, showing the flood extent and the water depth or level, and review them every six years [1]. Satellite data can add to these maps. Flood extents from the Sentinel-1 archive reach back to 2015 [4], and maps of sealed ground show where rainwater can no longer soak away [7]. Combined with digital terrain models, flood maps become more accurate and allow water depths to be estimated [6]. ### Forecasts and early warning The European Flood Awareness System (EFAS), part of the Copernicus Emergency Management Service, combines satellite data, weather and hydrological models and historical records. It gives probabilistic flood forecasts with lead times of up to ten days and notifies its partners, which include national, regional and local authorities. EFAS complements national and regional forecasting systems; it does not replace them [2]. ### Mapping the water during a flood Radar satellites such as Sentinel-1 deliver images in all weather, by day and night [3], so cloud does not block the view. The Global Flood Monitoring product maps the flood extent automatically from each new Sentinel-1 image [4]. For detailed maps of a specific event, authorised users can request the on-demand mapping of the Copernicus Emergency Management Service, free of charge [5]. **Figure:** Illustrative map, not real data. Areas at risk of flooding along the river, as a risk map would show them. ## What you get Flood data supports planning, preparation and response, each at its own pace. - **Flood extent maps** for past events and for an ongoing flood, as layers for your GIS. - **A flood history** of your area from the Sentinel-1 archive, to check where water has actually stood. - **Sealing maps** that show where heavy rain cannot soak away, as an input for drainage and heavy-rain planning. - **Forecast information** through EFAS for the authorities that are its partners. - **Rapid damage maps** after an event, when an authorised user activates the Copernicus Emergency Management Service for your area. ## Limits **Limits** - **Cities and forests are hard for radar:** Radar is not equally sensitive to flood water on every surface. Water between buildings and under dense vegetation is hard to detect \[6], and the automatic Global Flood Monitoring product gives each detection a likelihood value, so that uncertain results can be read with caution \[4]. - **Peaks can fall between passes:** A satellite maps the water at the moment it passes over. The highest water level may fall between two passes, and short flash floods after heavy rain may not be captured at all. - **Optical data needs a clear sky:** Optical images are limited by cloud \[6]. Radar fills the gap when cloud blocks the view. EFAS forecasts and notifications go to its partner authorities first and become public only after a 30-day embargo [2]. ## Related use cases - [Rapid damage mapping after disasters](https://leto.space/use-cases/disaster-rapid-mapping/): Damage maps and emergency communication after an event. - [Climate risk for properties](https://leto.space/use-cases/property-climate-risk/): Flood and wildfire risk for buildings and assets. - [Verifying insurance claims](https://leto.space/use-cases/claims-verification/): Checking claims after floods and storms. ## Find providers and get started Beyond the free Copernicus services, providers offer flood models, risk maps and monitoring services. The [Spacegraph](https://leto.space/spacegraph/) marketplace has a category for flood mapping and modelling. Whether you add a commercial service to the free ones depends on the detail, the speed and the format you need. We help you write those requirements so that providers can answer them, and compare the offers you receive. [Requirements and procurement](https://leto.space/consulting/procurement/) ## Frequently asked questions ### Which satellite data is used for flood mapping, and how quickly is it available? Radar data from Sentinel-1 is well suited, because the radar sees through cloud by day and night [3]. The Global Flood Monitoring product of the Copernicus Emergency Management Service derives a flood extent map from each new Sentinel-1 image automatically, in near real time, and holds flood information back to 2015 [4]. A new image exists only when a satellite passes over the area. ### Can a city request satellite maps during a flood? Only through an authorised user. The on-demand mapping of the Copernicus Emergency Management Service is free of charge and can be activated only by designated authorised users [5]. Who they are and how a request works are explained in the use case on [rapid damage mapping](https://leto.space/use-cases/disaster-rapid-mapping/). ### How do we start a pilot for flood risk mapping? Start with the decision the map should support: an emergency plan, land use planning, the protection of a specific asset or heavy-rain planning. Collect what already exists, such as the official hazard maps, local terrain data and records of past events, and test which satellite products add information to it. ## Sources 1. [Directive 2007/60/EC of the European Parliament and of the Council of 23 October 2007 on the assessment and management of flood risks, European Union, EUR-Lex, 2007-10-23](https://eur-lex.europa.eu/eli/dir/2007/60/oj/eng) 2. [Observer: How the EU Space Programme supports flood preparedness, the role of the European Flood Awareness System (EFAS), EU Space Programme (Copernicus Observer), 2025-01-29](https://eu-space.europa.eu/news/observer-how-eu-space-programme-supports-flood-preparedness-role-european-flood-awareness-system-efas) 3. [Sentinel-1, European Space Agency (ESA), accessed 2026-10-06](https://www.esa.int/Applications/Observing_the_Earth/Copernicus/Sentinel-1) 4. [Estimating Ensemble Likelihoods for the Sentinel-1-Based Global Flood Monitoring Product of the Copernicus Emergency Management Service, Krullikowski et al., IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, vol. 16, pp. 6917-6930, 2023](https://doi.org/10.1109/JSTARS.2023.3292350) 5. [About the Copernicus EMS On-Demand Mapping service, Copernicus Emergency Management Service, accessed 2026-10-07](https://mapping.emergency.copernicus.eu/about/) 6. [Recommended Practice: Flood Mapping with Sentinel-1 and Sentinel-2 Imagery and Digital Terrain Models, UN-SPIDER (United Nations Office for Outer Space Affairs), accessed 2026-10-06](https://un-spider.org/advisory-support/recommended-practices/recommended-practice-flood-mapping-sentinel-1-and-sentinel-2) 7. [Copernicus Land Monitoring Service: High Resolution Layer Imperviousness, accessed 2026-10-04](https://land.copernicus.eu/en/products/high-resolution-layer-imperviousness) Page: