FloodScore™ AAL Risk Rating Layers enable you to visualise property-level AAL-based flood risk ratings, and integrate them with your GIS systems for advanced flood risk assessment.

At a Glance

  • Provides an easy-to-compare AAL-based flood risk score at a 5m horizontal grid resolution
  • Can be used for commercial and residential risk rating
  • Covers 100% of properties in Great Britain and Northern Ireland
  • Considers risk from rivers, tidal waters and rainfall
  • Based upon a range of return periods
  • Uses hydrological and 2D hydraulic modelling and LiDAR wherever available
  • Validated against actual flooding and claims data from recent events
  • Regularly updated
  • Designed to support better Flood Receding decisions

FloodScore AAL Risk Rating Layers use the advanced flood modelling techniques developed for UKFloodMap4 ™. They incorporate the most current hydrology data from the Centre of Ecology & Hydrology, building stock data from Ordnance Survey, and the latest high-resolution LiDAR from the Environment Agency.

The AAL Risk Rating Layers are delivered as four layers: a layer for each of the three primary flood sources (tidal, surface, pluvial and fluvial) and a fourth layer which combines them. This makes it simple to consider specific flood sources in isolation, or get an aggregate view.

These layers show inundation extents, classified flood risk scores and average annual losses (AALs) at every location within the UK. They’re available as defended or undefended data layers. The risk scores and AALs are calculated from mean damage ratios and complex algorithms to provide a consistent flood score risk index.

We usually deliver the data in GIS raster format (typically compressed .tif or .img format), and it can be easily integrated into geospatial systems such as ESRI, LexisNexis and SpatialKey. We can also provide classified vector polygon and tabular look-up table versions. We can provide the data in British National Grid projection but also in other projections (eg WGS 1984). It can be used alongside council tax databases for enhanced portfolio and single-site analysis.

Request a free data sample to test


  • Improved loss ratios
  • Better accumulation control
  • More consistent flood underwriting
  • Quicker and easier to assess flood risk

Click to view the technical details

Data sources used

  • Ordnance Survey (OS) AddressBase Premium database for England, Scotland and Wales
  • Pointer address database for Northern Ireland
  • 2014/15 EA LiDAR (±0.15m nominal vertical accuracy) from the Environment Agency
  • The most current hydrological and river flow data from the UK’s leading flood research authority – the Centre for Ecology & Hydrology (CEH)
  • Mean damage ratios

Flood sources

  • Fluvial (rivers)
  • Tidal (sea/estuary/coastal)
  • Flash (pluvial/surface water)

Layers available

  • Flood risk rating (flood scores) for each flood source and combined flood score
  • Defended or undefended layers available

AAL calculation

To maintain national homogeneity, the mean damage to an ‘average’ property type has been used (combined buildings/contents) to estimate the losses against each return period.

Horizontal grid resolution

5 metres

Update frequency

Annual and after major flood events


Regularly validated and calibrated against actual flood events in the UK.

Approximately 6 million properties are at risk from some form of flooding in the UK.

Mark Nunns

Get in Touch

To get a quote or to discuss what you need, contact Mark Nunns

Call me on 0203 857 8543   or Email at mark.nunns@ambientalrisk.com

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