Flood Zones Explained

Contents 

• What are the different types of flood zones?
• How do I know if my property or development is in a flood risk area?
• How will proposed developments be impacted by flood zones? 
• What are the flood risk vulnerability classifications?
• Flood zones and climate change allowances
• Get a clearer picture

Flood zones are a guidance tool, formed by the Environment Agency, to demonstrate the probability of river and sea flooding in areas across England. 

The flood zones were produced to help developers, councils and communities understand the flood risks present in specific locations or regions, taking into account the presence of flood defences.

Despite being a very useful indicator of an area’s flood risk, the zones cannot tell you whether a location will definitely flood or to what severity. 

What are the different types of flood zones? 

There are four different flood zones that the Environment Agency uses to specify the flood risk of different areas in England. 

Flood zone 1: low probability

Locations determined to be in flood zone 1, have a low probability of flooding – less than 0.1% annual probability of river or sea flooding. 

Areas in flood zone 1 can also be described as: 

• Land having a less than 1 in 1,000 annual probability of river or sea flooding.

(Shown as ‘clear’ on the flood zone map – all land outside Zones 2 and 3)

Most land in England falls into Flood Zone 1, but that doesn’t mean no risk. Surface water flooding or smaller watercourses can still pose a threat, so site-specific assessments could still be required.

Flood zone 2: medium probability

Areas situated in flood zone 2 have a medium probability of flooding and have an annual probability of river or sea flooding between 0.1% and 1%.

Areas in flood zone 2 can also be described as: 

• Land having between a 1 in 100 and 1 in 1,000 annual probability of river flooding;

or

• Land having between a 1 in 200 and 1 in 1,000 annual probability of sea flooding.

(Land shown in light blue on the flood zone map)

Flood zone 3a: high probability

Unlike the previous two zones, flood zone 3 is divided into two sections: 3a and 3b. 

Flood zone 3 is distinguished as land which has a 1% or greater annual probability of river flooding or a 0.5% or greater annual probability of sea flooding. 

Areas in flood zone 3a can also be described as: 

• Land having a 1 in 100 or greater annual probability of river flooding;

or

• Land having a 1 in 200 or greater annual probability of sea flooding.

(Land shown in dark blue on the flood zone map)

Flood zone 3b: The Functional Floodplain

Flood zone 3b is also called the functional floodplain and refers to land which either stores water from rivers or the sea during flooding, or which allows such water to flow through in periods of flood. 

The government’s flood risk and coastal change planning guidance states that the ‘identification of functional floodplain should take account of local circumstances and not be defined solely on rigid probability parameters.’ 

Flood zone 3b usually refers to land that has a 3.3% or greater annual probability of flooding, regardless of the effective operation of flood risk management measures that are in place. 

This zone also refers to land which is ‘designed to flood’, which is the case for land that might only flood during more severe weather events. 

(Not separately distinguished from Zone 3a on the flood zone map)

Note that as of March 2025, the Environment Agency’s updated data (NaFRA2) includes a lot more detail such as local flood defences and climate change modelling, so even if your flood zone stays the same, the risk profile might have changed.

How do I know if my property or development is in a flood risk area?

There are two flood maps available for online users.

Flood Map for Planning

This map shows whether your site is in Flood Zone 1, 2 or 3, which is key for planning decisions and knowing if you need a Flood Risk Assessment (FRA).

The service enables users to type in an area’s address and discover which flood zone your site is located in. It shows the different types of flood risk the site could be affected by and the scale of each (rivers and sea, surface water, groundwater and reservoirs.)

It is important to note that the flood map for planning does not account for the potential impact which climate change may have upon future flood events. To see how climate change could increase the chance of flooding in an area, check your long-term flood risk.

Long-term Flood Risk Map

If you are worried about your area’s flood risk or want to know whether the location of a proposed development could be vulnerable to flooding in future, you can find out by using the Environment Agency’s long term flood risk map.

This flood map enables users to type in an area’s postcode and discover the level of long term flood risk for a specific address. 

The flood risk areas displayed in your search will be divided into risks from river and sea flooding and surface water flooding. 

Individuals or companies wishing to know the UK’s flood risk of areas outside of England can find out using the equivalent tools for Northern Ireland, Scotland and Wales. 

How will proposed developments be impacted by flood zones? 

According to the National Planning Policy Framework (NPPF), certain proposals for developments in flood zone 1 should be accompanied by a site-specific flood risk assessment. 

Such proposals include: 

• Projects where the site boundary is more than 1 hectare in size.
• Projects where the land has been identified as having critical drainage problems by the Environment Agency or Lead Local Flood Authority (LLFA).
• Projects where the site is at an increased risk of flooding from rivers or sea during its lifetime.
• Projects where the site could be susceptible to other sources of flooding and where development would increase such vulnerability.

The NPPF also states that all proposals for developments in flood zones 2 and 3 should be accompanied by a site-specific flood risk assessment. 

What are the flood risk vulnerability classifications? 

The flood risk vulnerability classification table is a system which dictates where proposed developments should and should not be built and if an Exception Test is required. 

Across the top of the table are five categories that are considered when a development’s vulnerability to flooding is assessed. These appear as follows: essential infrastructure, highly vulnerable, more vulnerable, less vulnerable and water compatible. 

If developments are proposed to be built in flood zone 1, an Exception Test is not required to approve the build and are the most likely to be approved. 

For developments proposed in flood zone 2, an Exception Test is only required if the development is deemed to be highly vulnerable to flooding. 

Exception Tests are also required for essential infrastructure proposed to be built in flood zones 3a and 3b and for developments in 3a if they would be more vulnerable to flooding. 

Proposed developments cannot be permitted in flood zone 3a if they would be classed as highly vulnerable to flooding, nor can they be approved if they would be located in flood zone 3b and classed as highly vulnerable, more vulnerable or less vulnerable to flooding. 

Flood Zones and Climate Change Allowances

The flood zones do not take account of the possible impacts of climate change and consequent changes in the future probability of flooding. Reference should therefore also be made to the Strategic Flood Risk Assessment and long-term flood risk service when considering location and potential future flood risks to developments and land uses.

The Environment Agency provides updated guidance on how to incorporate climate change allowances, which vary depending on:

• The source of flooding (rivers, surface water, sea)
• The vulnerability of the proposed development
• The lifetime of the development (typically 100 years for residential)

As of 2025, these allowances align with the most recent UK Climate Projections (UKCP18) and the Environment Agency’s new NaFRA2 modelling, offering a more detailed picture of future flood scenarios.

For example:

• River flow allowances have been adjusted based on local river basin data and emissions scenarios, with low, central, and upper-end allowances used depending on the flood zone and development type.
• Surface water and rainfall runoff allowances account for increases in peak rainfall intensity, especially important for SuDS design.
• Sea level rise allowances vary by coastal region and now include updated scenarios for both 2080 and 2100 planning horizons.

Developments in Flood Zones 2 and 3, or those identified at risk from surface water flooding, will need to demonstrate how these future climate scenarios have been accounted for in design, particularly where safe access, finished floor levels, or flood mitigation measures are concerned.

The EA made revisions in May 2022 to the peak flow rate of rivers in various catchments across the country based on climate change predictions. Read their guidance online.

This translates to new guidance for councils and developers on the relevant peak rate to use in each flood zone:

Flood zone 2 or 3a:

• Essential infrastructure – use the higher central allowance
• Highly vulnerable – use the higher central and upper end to assess a range of allowances
• More vulnerable – use the central allowance
• Less vulnerable – use the central allowance
• Water-compatible – use the central allowance

Flood zone 3b

• Essential infrastructure – use the higher central allowance
• Highly vulnerable – development should not be permitted
• More vulnerable – development should not be permitted
• Less vulnerable – development should not be permitted
• Water-compatible – use the central allowance

We’ve collected Strategic Flood Risk Assessments from different local authorities and you can find further information in the GeoSmart Knowledge Hub.

Get a Clearer Picture

GeoSmart understands how river, surface and groundwater flooding can affect property and development sites.  

Our expert flood risk consultants will advise on flood zones and constraints, as well as potential vulnerabilities that could impact on your client’s permitted development project.

For more information about our flood risk assessments, please get in touch today.