Flooding Hazard

Flooding is a major hazard in Great Britain. An estimated five million households - one in five - are at risk to flooding. And annual damage from flood is estimated at between £500 million and £1 billion each year.

Data from Met Office UK Climate Projections (UKCP) indicate that the UK is likely to receive more bouts of heavy rain more frequently as temperatures rise as a result of climate change. The number of flood events is likely to increase, and along with it, the potential for loss and damage. Data for different types of flooding (groundwater, surface, river and coastal flooding) is key to managing the risk both now and in the future.

We supply UK flood hazard and risk mapping in many formats from leading specialists JBA Risk Management and Royal Haskoning (Twinn, Ambiental). We supply data and web services to planners, developers, lenders and insurers alike for assessing the likelihood of flooding and mitigating risk.

Since April, 2022, it has been mandatory for the largest UK-registered companies and financial institutions to disclose climate related financial information inline with TCFD recommendations (Task Force on Climate-Related Financial Disclosures).

Our Flood hazard and risk mapping and data identify current and future risk from climate-related factors, such as flood, vital to that activity.

Our climate intelligence and web services can drive your automated outputs, feed into consumer-facing reports, and give you the foundations on which to build strong and measurable insights about climate-related, physical and transitional risk management.

JBA 5m GB Flood Map provides vector flood extents and banded depths for river, surface water, coastal and groundwater (chalk areas) flood sources. The data is presented at 5m resolution for a range of return periods (annual exceedance probabilities) from 1-in-20 to 1-in-1,000 for defended and undefended scenarios in Great Britain. Data for Northern Ireland is also available on request.

JBA 5m GB Flood Map is created from simulated rainfall-runoff processes and the JBA 'J-Flow' hydraulic modelling software, which simulates flood inundation across large areas. The simulations consider how water flows across a digital elevation model taking into account land cover data and is based on approaches from the Flood Estimation Handbook (the national standard for flood estimation in the UK). TUFLOW kis used for coastal storm/surge modelling.

JBA 5m GB Flood Map is intended for customers to make informed decisions about flood hazard in their area of interest. The flood extent and banded-depth information provides a visual representation of flood hazard and helps in various applications, including:

• Insurance - to understand the likelihood of flood damage in specific areas;
• Urban Planning/Development - to identify areas where flood defences are required or where mitigation/resilience measures should be implemented (e.g., raising buildings, improving drainage);
• Emergency Response Planning to identify potential evacuation routes and understand where resources might be needed most during a flood event;

JBA 5m GB Flood Map is updated annually.

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Technical Details

Supplier: JBA
Update Cycle: Annual
Coverage: Great Britain
Scale
Formats Available: SHP, TAB, GDB, DWG
Stated Accuracy
Stated Accuracy
Stated Accuracy
Licence Options: Annual
Delivery Timescale: Within minutes

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Twinn Floodmap Climate

Twinn Floodmap Climate is a high-resolution, climate adjusted flood map using local hydrological data, high-resolution terrain models, and climate uplift data to create a view of current and future hazards (fluvial, pluvial and tidal). It provides a view of current and future, undefended flood hazards (fluvial, pluvial and tidal) for three return periods, three time horizons and three emissions scenarios to estimate potential impact on projects and asset portfolios and to satisfy ESG disclosure requirements.

• Undefended
• Climate Epochs (2020’s, 2050’s and 2080’s)
• Emissions Scenarios (RCP2.6, RCP4.5 and RCP8.5)
• Return Periods (1-in-30, 1-in-100 and 1-in-500 years)

Twinn Floodmap Climate also indicates expected sea level rise (low and high tide lines) and areas subject to inundation due to sea-level rise rather than as a result of a specific flood event. Plus river-bank and erosion potential for each 100-metre river segment.

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Twinn FloodMap4™

Twinn FloodMap4™ is a 5-metre resolution, property-level, flood risk model for the whole of Great Britain. It is used by planners, lenders, developers, asset owners, insurers, government agencies and emergency responders to visualise, assess, and mitigate potential flood risk. Flood maps for Northern Ireland and the Channel Islands (Guernsey, Jersey) are also available and are licensed separately.

FloodMap4™ considers multiple flooding sources (fluvial, pluvial, groundwater and tidal), each modelled separately to indicate the likely extent and depth of flooding for six return periods (annual exceedance probabilities). The model is derived using LiDAR and Bluesky’s Digital Terrain Model elevation data and models 30% more rivers than other products by modelling further up the catchment area. Guided by the UK Centre for Ecology and Hydrology methodology, it simulates complex river (fluvial) flood flows, tidal storm/surge, and intense rainfall-driven (pluvial) flood events using land cover data and building outlines from OS VectorMap District.

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Technical Details

Supplier: Twinn (formerly Ambiental)
Update Cycle: Annually (April)
Coverage: GB (separate datasets are available for NI and Channel Islands)
Scale
Formats Available: TIF, SHP
Stated Accuracy
Stated Accuracy
Stated Accuracy
Licence Options: Minimum 12 month licence (discounts applied to 3-year contract terms)
Delivery Timescale: Same day (depending on extent ordered)

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OS MasterMap Water Network Layer

OS MasterMap Water Network Layer is a detailed, heighted water network, showing the flow and course of every river, stream, lake and canal in Great Britain.

The vector link and node network provides a detailed centre line following the curve of the waterway and includes coordinates of watercourse sources and where they meet (with flow direction, gradient, length and width anywhere along its length). The product also illustrates underground watercourses (inferred from entry and exits), details the heights of watercourses in relation to sea level and provides the OS topographical identifier (TOID) and Environment Agency or Scottish Environment Protection Agency catchment name and ID.

OS MasterMap Water Network Layer is useful in 2D and 3D modelling for planners, surveyors and engineers, particularly in combination with Ordnance Survey datasets for use cases such as:

• Flood risk and mitigation planning;
• Flood response planning and execution;
• Flood modelling for insurance and land and property;
• Asset management and protection;
• Environmental impact analysis.

OS MasterMap Water Network Layer is projected in the ESPG 7405 OSGB36 / British National Grid + ODN (specifies that the Z value is Ordnance Datum Newlyn).

Note: This product will become End of Life on 31Mar2626 (OS will cease to maintain or publish updates). The final update will be provided in January 2026. It may be more appropriate, therefore, to consider the use of OS National Geographic Database (NGD) Water Theme.

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OS NGD Water Theme

OS National Geographic Database Water Theme replaces OS MasterMap Water Network Layer. The 'theme' comprises two ‘collections’ (Water Network and Water Features) which in turn consist of nine feature types providing geometry, feature classification and other attribution for watercourses, lakes, drains, springs and intertidal watercourses in Great Britain.

OS NGD Water Network provides a three-dimensional structured link and node network of GB watercourses, representing general alignment and connectivity of permanent water with flow direction and catchment name.

OS NGD Water Features include river basin district and waterbody catchment features as published by national water bodies. Areas of permanent water are listed as point or polygon features depending on area.

Licence: PDF

Technical Details

Supplier: Emapsite
Update Cycle: Quarterly
Coverage: GB
Scale: 1:1250-1:10 000
Formats Available: SHP, GZ, GML Tile
Stated Accuracy
Stated Accuracy
Stated Accuracy
Licence Options: Annual
Delivery Timescale: Within 24 hours

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JBA GB UPRN Flood Data

JBA GB UPRN Flood Data provides flood hazard information for each property defined by a 10-metre buffer around each Ordnance Survey residential unique property reference number point (UPRN). The buffered area represents a standard residential building with adjacent area (e.g. garden) and is used by planners, property developers, lenders and insurers alike to understand the likelihood of flooding.

JBA GB UPRN Flood Data has been improved with updated elevation data, updated land use data and updated hydrology methods accounting for non-stationarity in peak flow estimation. The data includes:

• Maximum flood depth per return period (annual exceedance probabilities) at each property for undefended river, surface water, defended and undefended coastal flood sources;
• JBA Matrix flood scores for undefended river, undefended surface, groundwater chalk flood (where available) defended and undefended coastal flood sources
• Unflood' index rating (height above the nearest area at risk of flooding), 'Floodability' index rating (a colour rating) and the standard of protection provided by river and surface water defences where present.

Northern Ireland data available on request.

JBA GB Postcode Flood Data

JBA GB Postcode Flood Data provides flood hazard information for building footprints with all postcodes in Great Britain (including 'vertical streets'). Building footprints within each postcode area are taken from Ordnance Survey Open Map Local and buffered by 5 metres to include grounds around the building. The data is used by planners, property developers, lenders and insurers alike to understand the likelihood of flooding in a postcode area and includes:

Flood depth data (minimum, maximum and mean flood depth in metres) per return period (annual exceedance probabilities) for each postcode and flood source.

JBA Flood Matrix flood scores per return period for each flood type, plus an overall, 'combined' flood score for defended and undefended scenarios.

Also includes 'Unflood' index rating (height above the nearest area at risk of flooding), 'Floodability' index rating (a colour rating) and the standard of protection provided by river and surface water defences where present.

Northern Ireland data available on request.

Technical Details

Supplier: JBA
Update Cycle: Annual
Coverage: Great Britain
Scale
Formats Available: CSV
Stated Accuracy
Stated Accuracy
Stated Accuracy
Licence Options: Annual
Delivery Timescale: Within 24 hours

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Twinn FloodScore Climate

FloodScore Climate provides a view of climate-related, property-level flood risk information for Great Britain. The product provides an estimate of the likelihood and severity of climate-related flood hazards affecting each individual property and is intended for use by property investors, mortgage lenders, property owners (e.g. Housing Associations) and insurers.

FloodScore Climate adopts UK Climate Projections 2018 (UKCP18) data to model future climate. This is modelled in three epochs for four future CO2/Greenhouse Gas emissions scenarios (Representative Concentration Pathways – RCP) and six return periods. The product provides estimates for flood depths for each property address in defended and undefended scenarios along with undefended risk ratings (i.e. FloodScore), average annual loss (AAL) and annual damage ratio (ADR) information for each flood source.

The product enables customers to estimate the longer term view of flood risk for their projects and asset portfolios and to satisfy disclosure requirements of various Environment, Social Governance (ESG) reporting frameworks.

The product includes UK FloodScore (the current view of flood risk) - available separately.

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Twinn FloodScore

Based on Twinn FloodMap4, Twinn FloodScore indicates the current view of the likelihood and severity of climate-related flood hazards affecting individual properties (fluvial, pluvial and tidal). The provides estimates for flood depths in defended and undefended situations along with undefended risk ratings, average annual loss (AAL) and annual damage ratio (ADR) values for each flood type. Where a property address point is not situated within a modelled flood extent, the distance to the nearest floodplain is indicated.

Each property address is considered as a buffered point (Lat/Long) depending on property type. The maximum flood depth within the buffered area is considered for each flood source and each return period and the likelihood of flooding is expressed as a return period which is a measure of the average recurrence interval of a specific flood event. The property buffer is used to avoid understating the level of risk where a property may be shown to be flooding within its footprint, but the flood extent does not intersect the property centroid.

FloodScore estimates property-level loss in Pounds Sterling (£) for each flood source and return period based on standard industry figures of rebuild/reinstatement costs for a national average residential property. Values are provided for average annual loss (£AAL), annual damage ratio (ADR) and an overall risk rating.

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Technical Details

Supplier: Twin (formerly Ambiental)
Update Cycle: Twice per year
Coverage: GB
Scale
Formats Available: CSV
Stated Accuracy
Stated Accuracy
Stated Accuracy
Licence Options
Delivery Timescale: Next day

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CSV

BGS Groundwater Flooding is a 1:50,000 scale dataset indicating the degree to which areas may be susceptible to groundwater flooding. Data is presented in four groundwater flooding classes, including surface and sub-surface, with a confidence dataset and advice on what action to take based on the classification.

Groundwater flooding is the emergence of groundwater at the ground surface. It can occur in a variety of geological settings including valleys in areas underlain by Chalk, and in river valleys with thick deposits of alluvium and river gravels. Groundwater flooding happens in response to a combination of already high groundwater levels (usually during mid- or late-winter) and intense or unusually lengthy storm events. Groundwater flooding often lasts much longer than other flooding types and usually persists long after the weather event which triggered it causing significant social and economic disruption to affected areas.

Data is available in Shapefile or Tab file format.

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Technical Details

Supplier: British Geological Survey
Update Cycle: Annual
Coverage: GB
Scale
Formats Available: SHP
Stated Accuracy
Stated Accuracy
Stated Accuracy
Licence Options: Annual
Delivery Timescale: Same day

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OS 1:50 000 Raster

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WHAT IS THIS THING ABOVE THIS TEXT?

JBA 5m GB Megaraster contains flood hazard data at 5m resolution for all flood sources for Great Britain (river, surface, coastal, groundwater/chalk), including Isle of Man and the Channel Islands. It provides an efficient way to view and interrogate all the information contained in JBA’s 5m resolution flood maps for any location rather than having to analyse each spatial layer separately.

JBA 5m GB Megaraster provides scores from the JBA Matrix Score system for every 5-metre grid cell, for every flood source, for multiple return periods (annual exceedance probabilities). It also presents flood extent and banded depth data and summarises the likelihood of flood depth/intensity with a combined flood score (0/low to 53/high).

• Separate raster datasets are provided for defended and undefended scenarios
• Data for Northern Ireland on request
• Data updated annually

Note: The 'JBA Matrix' is a series of tables providing qualitative ratings of flood hazard and is used as an indicator of flood hazard at a given location.

Technical Details

Supplier: JBA
Update Cycle: Annual
Coverage: Great Britain
Scale
Formats Available: SHP, TAB, GDB, DWG
Stated Accuracy
Stated Accuracy
Stated Accuracy
Licence Options: Annual
Delivery Timescale: Within minutes

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Data samples are for evaluation purposes only. JBA accepts no liability.

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Twinn Groundwater FloodMap is a screening tool for identifying flooding as the water table rises, likely to affect surface and sub-surface assets (e.g. basements). Combines flood hazard data for chalk-areas and national-scale areas for each return period. Validated and calibrated regularly using information from actual flood events.

Groundwater FloodMap is a companion dataset to FloodMap4 and provides an even more comprehensive view of flood hazard. It combines comprehensive data on geology, permeability, and historic groundwater levels to provide insight into the actual risk of groundwater flooding for a 1 in 100-year return period using a 5-point scoring system from negligible (0) to high (4). The basement impact model also indicates where groundwater levels may rise to coincide with basement structures (i.e. 2-3 metres below ground level).

Why is the product important?

Twinn Groundwater FloodMap provides a view of a flood hazard which is often overlooked. Groundwater flooding is a significant threat to construction projects, utility infrastructure and property value generally and usually persists long after the weather event that triggered it. Twinn Groundwater FloodMap is useful for construction companies, property developers, property investors and mortgage lenders, property owners, asset managers, utility companies and insurers.

Please note: The Sample to the right is for evaluation use only.

Buy Twinn Groundwater Flood Map

Technical Details

Supplier: Twinn (formerly Ambiental)
Update Cycle: Annually
Coverage: GB
Scale
Formats Available: TIF, SHP
Stated Accuracy
Stated Accuracy
Stated Accuracy
Licence Options
Delivery Timescale: Same day

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BW TIF

This dataset is suitable for those involved in the planning and design of sustainable drainage systems (SuDS) and for those who approve SuDS planning applications within local authorities.

The dataset provides a preliminary indication of the suitability of the ground for infiltration drainage systems such as soakaways, infiltration basins, infiltration trenches and permeable pavements. It should be complemented by site investigation.

The selection and design of an appropriate system depends on the properties of the ground including:

The presence of severe constraints that must be considered prior to planning infiltration
The drainage potential of the ground
The potential for ground instability when water is infiltrated
The protection of groundwater quality

The BGS Infiltration SuDS map is based on 15 nationally derived subsurface property datasets, some of which are a result of direct observations, whilst others rely on modelled data. It allows consideration of the subsurface permeability, the depth to groundwater, the presence of geological floodplain deposits, the presence of artificial ground, ground stability (soluble rocks, collapsible ground, compressible ground, running sand, shallow mining, landslide and shrink–swell clays), potential for pollutant attenuation and the Environment Agency's source protection zones.

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Technical Details

Supplier: British Geological Survey
Update Cycle
Coverage: GB
Scale: 1:50,000
Formats Available: SHP, TAB
Stated Accuracy
Stated Accuracy
Stated Accuracy
Licence Options: Annual
Delivery Timescale: Same day

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SuDS (Summary) sample: TAB, SHP

SuDS (Detailed) sample: TAB, SHP

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JBA 5m Floodability Data provides a descriptive indication of the likelihood of flooding from river, surface water and coastal flood types using a colour-coded rating scale at 5-metre resolution (green/low to black2/very high). Includes ‘Unflood Data’ indicating the height of each 5m grid cell above, and distance from, the nearest area of flooding.

JBA 5m Floodability Data flood score ratings are defined for each 5-metre grid cell in Great Britain using flood depth information from three flood types (river, surface and coastal) and for a range of return periods (1-in-20 years to 1-in-1,000 years) in defended and undefended scenarios:

• Defended - compiled from data for defended coastal, undefended river, undefended surface water, defended river areas (DRA) and defended surface water areas (DSWA

• Undefended - compiled from data for undefended coastal, undefended river and undefended surface water.

JBA 5m Floodability Data is useful as a screening tool when seeking an initial view on the likelihood of flooding at a given location. Where a higher rating score is indicated, further investigation is advisable (e.g. a site inspection). The dataset is updated on an annual basis in line with the flood map updates.

Technical Details

Supplier: JBA
Update Cycle: Annual
Coverage: Great Britain
Scale
Formats Available: CSV
Stated Accuracy
Stated Accuracy
Stated Accuracy
Licence Options: Annual
Delivery Timescale: Within 24 hours

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Download Samples

Data samples are for evaluation purposes only. JBA accepts no liability.

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SHP0

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Flooding Hazard

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JBA 5m GB Flood Map

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Twinn FloodMap Climate

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OSMM Networks Water Layer /OS NGD Water Theme

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JBA GB Flood Data (UPRN/Postcode)

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Twinn FloodScore/Climate

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BGS Groundwater Flooding

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JBA 5m GB Megaraster

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Twinn Groundwater Flood Map

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BGS SuDS

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JBA 5m GB Floodability

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