What Surface Water Flood Forecasting Means for Developers and Planning Applications (SWFFIP)

FPS Environmental | May 2026

The UK has just taken a significant step forward in how it forecasts surface water flooding. In April 2026, the Flood Forecasting Centre published the results of the Surface Water Flood Forecasting Improvement Project (SWFFIP), a three-year programme that has reshaped how short-notice flood events are predicted and communicated.

If you’re planning a development, preparing a planning application, or advising clients on either, the findings matter. Surface water risk is being looked at more carefully than ever, and the evidence base behind that scrutiny has just got tighter.

Why this matters now

Surface water flooding is no longer a “nuisance” risk. The latest National Flood Risk Assessment (NaFRA) shows that around 4.6 million properties in England are now at risk from surface water, a 43% rise on the previous assessment. There are now three times as many properties at high risk from surface water flooding than from rivers and the sea combined.

That shift is already changing how local planning authorities, lead local flood authorities and statutory consultees look at planning applications. Schemes that might once have sailed through are now being asked harder questions about runoff, drainage and what happens during short, intense storms, the kind of events that climate change is making more common.

What SWFFIP actually is

SWFFIP is a Flood Forecasting Centre-led initiative that ran for three years and finished its main reporting phase in early 2026. Its goal was simple: improve the country’s ability to forecast surface water or rapid flooding, so emergency services, councils and the public get more useful warnings, sooner.

The Rapid Flood Guidance (RFG) service

The most visible output is the Rapid Flood Guidance service, which is now operational and has been committed to until at least 2028. RFG gives emergency responders an impact-based forecast, not just “rain is coming” but this is the likely level of disruption to people, property and infrastructure.

Better hazard and impact modelling

Behind the scenes, SWFFIP has improved the tools forecasters use, including:

• The Surface Water Flooding Hazard Impact Model (SWFHIM), which forecasts surface water flood risk from around six hours to three days ahead, broken down by likely impact severity.
• Proof-of-concept trials for nowcasting tools, the 0-to-6 hour window where decisions about evacuations, road closures and equipment deployment get made. This included a new nowcast version of SWFHIM and the Forewarns model developed by the University of Leeds.

Why developers and planning applicants should care

You might be wondering what a forecasting upgrade has to do with planning permission. The answer is: quite a lot.

Surface water risk is being scrutinised more closely

When the national risk picture sharpens, the local one does too. NaFRA outputs feed directly into the maps and datasets that planners, lead local flood authorities and statutory consultees use when reviewing applications. The same data that drives the new forecasting tools is the data that will decide whether your site is treated as a surface water flood risk, and how robust your application needs to be.

Planning authorities want robust, site-specific evidence

Generic, template-driven flood and drainage submissions don’t go down well anymore. Authorities increasingly expect site-specific assessment, looking at the actual catchment, soils, levels, runoff routes and proposed layout.

Better forecasting raises the bar for drainage design

If forecasts can pinpoint impact at finer spatial resolution, expect drainage strategies to be held to a similar standard. “We’ll discharge to the sewer” is rarely an acceptable answer in 2026. Authorities will want to see the drainage hierarchy properly applied: reuse first, then infiltration, then surface water bodies, and only then piped systems.

How this changes what you need to submit

There are three documents that will increasingly determine whether your application clears the surface water hurdle.

Flood Risk Assessment (FRA) for development

A Flood Risk Assessment shows how flood risk has been considered for your site, including surface water, and how the development manages and, where possible, reduces that risk. With surface water now sitting alongside rivers and the sea on the National Risk Register, FRAs that ignore pluvial risk will increasingly come back marked for revision.

FPSE’s Flood Risk Assessment service for developers is built around exactly this scrutiny, producing NPPF compliant FRAs that anticipate the questions planning authorities and the Environment Agency will ask.

Surface Water Drainage Strategy

A Surface Water Drainage Strategy, sometimes called a SuDS Strategy, is now expected on almost any development that affects drainage. It sets out how rainfall will be managed across the site once it’s built, demonstrating the drainage hierarchy has been followed and that runoff won’t be pushed onto neighbouring properties or overload existing infrastructure.

Done properly, it isn’t a tick-box. It’s an engineering document that:

• Reviews existing drainage and the wider catchment
• Calculates greenfield and post-development runoff
• Assesses soil conditions and infiltration potential
• Proposes SuDS features (swales, basins, permeable paving, rainwater reuse and more)
• Demonstrates compliance with the NPPF and local authority guidance

Working with planning consultants

For planning consultants, the practical message is straightforward: the surface water side of an application is no longer a minor concern. Engaging flood and drainage expertise early, before site layout is fixed, is now the difference between a smooth approval and a costly redesign. FPSE works alongside planning consultants to embed flood and drainage thinking into proposals from day one.

Looking ahead to 2029

The next phase of work, the follow-on three-year project, is expected to bring nowcasting and impact-based forecasting fully into operational use by 2029. Expect that to translate, over time, into:

• More granular surface water flood risk data feeding into planning policy
• Higher expectations on the evidence base in FRAs and drainage strategies
• More confident challenge from statutory consultees when submissions are thin

In other words, developments that take surface water seriously now will save time, cost and pressure later.

How FPS Environmental can help

FPS Environmental has been advising developers, architects and planning consultants on flood and drainage for over a decade. Our team can help you:

• Produce a planning-ready Flood Risk Assessment for development
• Prepare a site-specific Surface Water Drainage Strategy
• Support planning consultants on complex schemes where flood and drainage constraints are part of the picture

If you’re at the early stages of a planning application, or you’ve had a response from the LPA flagging surface water concerns, a conversation is usually all it takes to map out the right approach.