Flood Warning Gap
How much notice do flood warnings give?
It depends on the flood type. For rivers and the coast, the Environment Agency’s free service gives notice through its ‘Flood Alert’, ‘Flood Warning’ and ‘Severe Flood Warning’ tiers, with lead time varying by location and river response. For surface water flooding, most properties get no advance property-level notice at all, Previsico provides up to 48 hours.
Last updated September 14, 2026
The official tiers
The official flood warning tiers
These tiers give genuine notice for river and coastal flooding. How far ahead depends on how quickly the river or coast responds to rainfall and tides.
Flood Alert
Flooding is possible, be prepared. Issued earliest, over the widest area.
Flood Warning
Flooding is expected, act now.
Severe Flood Warning
Danger to life, immediate action needed.
Why surface water flooding gives so little notice
Surface water floods form fast, close to where the rain falls, so by the time general weather forecasts translate into an actual flood it is often too late to act. Rainfall forecasts alone lack the local drainage, topography and antecedent-condition detail that decides whether a specific property floods.
That lag is familiar to teams who manage exposed infrastructure directly: asset operators describe river flood warnings as often arriving only once it is already too late to move people or equipment.
The Previsico difference
48 hours of property-level notice
Enough notice to move assets, protect a site and mitigate the loss, not just record it.
See the risk to every asset, 48 hours out
Previsico forecasts surface water flooding up to 48 hours ahead, per property, likelihood, severity and timing, refreshed hourly at 25m resolution. Previsico tells you when to act; risk models tell you where the risk is.
- 48 hours’ advance notice, per property
- Refreshed hourly, at 25m resolution
- Likelihood, severity and timing, not just a static risk score
Verified specifications
The numbers behind the 48-hour warning
Previsico’s surface water warning window (product specification).
Every property-level forecast updates hour by hour.
The scale at which each property-level forecast is calculated.
Frequently asked questions
It depends on the flood type. The Environment Agency’s free service gives river and coastal notice through its Flood Alert, Flood Warning and Severe Flood Warning tiers, with lead time varying by location. For surface water flooding, most properties get no advance property-level notice at all, Previsico provides up to 48 hours.
A Flood Alert means flooding is possible and residents should be prepared. A Flood Warning means flooding is expected and action is needed now. A Severe Flood Warning, the Environment Agency’s highest tier, means there is a danger to life and immediate action is required. All three cover river and coastal flooding.
Historically, very little. Surface water floods form fast and close to where the rain falls, so by the time it is visible on the ground it is often too late to act, and the Environment Agency’s free warnings do not cover it at property level. Previsico closes that gap with up to 48 hours of property-level notice.
Up to 48 hours ahead, per property, refreshed hourly at 25m resolution, enough notice to move assets, protect a site and mitigate the loss. See the Flood Intel Platform for how the forecast is built.
Turn notice into action for your sites.
See your own sites on the platform, or get a free flood-risk assessment for your portfolio. No obligation.