Flood forecasting answers
Clear, direct answers on surface water flooding, flood alerts and how Previsico forecasts floods at property level. Can't find what you need? Get more info or request a demo below.
Last updated October 1, 2026
Surface water flooding
Surface water flooding happens when heavy rainfall overwhelms drains and the ground, pooling and running across land before it reaches a river or the sea. It is the most common form of flooding in the UK, putting an estimated 4.6 million properties at risk (Environment Agency, NaFRA2).
Read more: Surface water flooding in the UK (flood-warning-gap/surface-water-flooding-uk).
Surface water is the majority of UK flooding. The Environment Agency's NaFRA2 assessment puts 4.6 million properties at surface-water risk, more than the 2.4 million at risk from rivers and the sea. That figure rose 43% on the previous national assessment.
Read more: Surface water flooding in the UK (flood-warning-gap/surface-water-flooding-uk).
No. River and coastal flooding come from watercourses or the sea overtopping their banks. Surface water flooding forms wherever rainfall collects faster than drains and ground can absorb it, often far from any river, which is why it behaves, and needs warning, differently.
Read more: The flood alert gap (flood-warning-gap).
Surface water floods develop fast and locally, so they are hard to predict without property-level modelling. Around 90% of organisations have no flood plan, and most learn of a flood only when water is already on site, leaving no time to move assets or mitigate the damage.
Read more: The cost of flooding (resources/cost-of-flooding).
Flood warnings and the alert gap
The Environment Agency's free flood warnings cover river and coastal flooding only. Surface water flooding sits outside that service, so millions of at-risk properties get no official advance warning for the most common form of UK flooding. Previsico was built to close that gap.
Read more: Does the EA warn about surface water? (flood-warning-gap/environment-agency-surface-water).
The flood alert gap is the absence of official advance warning for surface water flooding. Free national warnings cover rivers and the coast, but not the pluvial flooding that puts 4.6 million UK properties at risk, leaving organisations exposed to the losses nothing warns them about.
Read more: The flood alert gap (flood-warning-gap).
Official river and coastal warnings typically give a few hours' notice. Previsico issues property-level surface water alerts up to 48 hours ahead, refreshed hourly as the forecast sharpens, giving teams time to move assets, deploy resources and act before the water arrives.
Read more: How much notice do warnings give? (flood-warning-gap/flood-warning-lead-times).
Work is under way to improve national surface water forecasting, but no free service currently warns at property level. Until one exists, organisations that need site-specific surface water alerts rely on operational services like Previsico rather than general national forecasts.
Read more: When will national warnings arrive? (flood-warning-gap/national-surface-water-forecasting).
How the forecasting works
Previsico runs live, physics-based hydrodynamic simulations of how water moves and pools during a storm. Its FloodMap+ engine combines ensemble rainfall forecasts, elevation, drainage and ground conditions to produce property-level surface water alerts up to 48 hours ahead, refreshed hourly.
Read more: The technology (technology).
Hydrodynamic flood modelling simulates the real physics of water flowing and accumulating across the ground, rather than overlaying rainfall on static maps. It accounts for local drainage, terrain and how saturated the ground already is, giving a far more realistic picture of where and when surface water will flood.
Read more: The technology (technology).
FloodMap+ is Previsico's peer-reviewed hydrodynamic forecasting engine, developed from two decades of Loughborough University research and published in Nature, Nature Water and Hydrological Processes. It powers every Previsico forecast, simulating surface water at property level rather than estimating risk from static maps.
Read more: The technology (technology).
Probabilistic flood forecasting shows the likelihood and severity of flooding, not a single yes/no answer. Previsico generates it from hundreds of pre-computed simulations and ensemble rainfall data, reporting likelihood (low/medium/high), severity and median depth per asset, so teams prioritise where to act.
Read more: Flood Intel Platform (intel-platform).
Instacast is Previsico's 24-hour lookback. Using the most recent observed radar rainfall, it models where surface water flooding has likely already formed, at the same property-level detail as the forecast, bridging what has already happened and what may happen next for immediate situational awareness.
Read more: Flood Intel Platform (intel-platform).
Previsico forecasts at property level detail, refreshed every hour up to 48 hours ahead, reporting likelihood, severity and median depth for each asset. Managed radar sensors and cameras verify live water levels on the ground, and the engine calibrates over time against sensor data and observed events.
Read more: The technology (technology).
The platform, sensors and data
The Flood Intel Platform is Previsico's platform for operational flood forecasting. It combines probabilistic property-level forecasts, a 24-hour lookback (Instacast) and optional managed ground-truth sensors and cameras, delivered through a web dashboard, email, text message and a REST API.
Read more: Flood Intel Platform (intel-platform).
Previsico manages non-contact radar flood sensors and cameras deployed at your sites. They measure water levels to millimetre precision in near real time and feed straight into the platform, verifying forecasts on the ground so an early alert becomes a confirmed, actionable signal.
Read more: The technology (technology).
Yes. The Previsico REST API gives automated access to every dashboard insight, asset-level alerts, hourly risk timelines, lookback data, flood-map layers and sensor readings. Responses are JSON (map tiles as Mapbox Vector Tiles) and assets upload as GeoJSON, so you can build Previsico's flood intelligence into your own systems.
Read more: The Previsico API (intel-platform/api).
No. Products like Fathom, JBA and RMS produce static, long-term risk maps for pricing. Previsico is operational: it forecasts live surface water flooding at property level up to 48 hours ahead, so teams can act during an event, not just estimate risk over decades.
Read more: The technology (technology).
Each answers a different question. A free risk map shows static, long-term likelihood for pricing, not what is happening right now. Government warnings from the Environment Agency cover river and coastal flooding only, not surface water, pluvial or flash flooding. A weather forecast tells you it might rain, not which asset will flood, when, or how severely.
Previsico turns all three into one operational answer: live, property-level surface water forecasts up to 48 hours ahead, refreshed hourly, so you know exactly where to act, not just where risk is theoretically higher.
Read more: The flood alert gap (flood-warning-gap).
Previsico is a UK company (Loughborough) and its camera units are built to be GDPR compliant. The API uses key-based authentication with separate production and development keys. For full detail on how we process and protect data, see our privacy policy or ask our team.
Read more: Privacy policy (privacy-policy).
Who it's for and getting started
Previsico is used by insurers, brokers and large organisations with flood-exposed property, alongside utilities, infrastructure operators, housing providers and councils. Insurers and brokers use it to price and place flood risk; asset owners use it to protect sites and mitigate claims.
Read more: Solutions (solutions).
Insurers use property-level data to price, place and manage flood-exposed risk and mitigate claims, Liberty Specialty Markets has used it as a policy condition for over four years. Brokers use it to make flood-exposed clients insurable and remove business-interruption exposure before a claim.
Read more: For insurers (solutions/insurers) and for brokers (solutions/brokers).
The UK is Previsico's primary market, but the Flood Intel Platform is built to be global-ready and already operates beyond it. FloodMap+ uses the best available elevation and rainfall data for each region, so coverage scales from a single UK site to a global property book.
Read more: Commercial property (solutions/corporate-portfolios).
Previsico is a B2B SaaS subscription (the Flood Intel Platform), scoped per deployment, the number of assets and regions, and whether you add managed ground-truth sensors. There is no public price list; request a demo and our team will scope a quote for your portfolio.
Read more: Request a demo (request-demo).
Request a demo and our team will show your own sites on the platform, with no obligation. You can also book a free flood risk assessment to see where your property-level surface water exposure sits before you commit.
Read more: Request a demo (request-demo) or the free flood risk assessment (free-flood-risk-assessment).
Still have a flood question?
Talk to our team or see Previsico on your own sites.