Gera Flood Exposure Score (GFES) — Methodology

What the score measures

The Gera Flood Exposure Score (GFES) is a 1–10 index of the number of Environment Agency (EA) flood warning areas attributed to a county in England. The EA creates flood warning areas wherever it judges there to be a significant risk of flooding from rivers or the sea. More EA warning areas in a county directly reflects greater flood exposure. A score of 10 indicates the highest density of EA-monitored flood warning zones; a score of 1 indicates the lowest.

The GFES is a relative density index, not an absolute probability of flooding. It is useful for comparing counties and for informing conversations about home insurance, flood preparation, and property risk — but it should not replace an individual property flood risk check (available free via the EA's Long Term Flood Risk service).

Data source

Formula

1. Fetch all flood warning areas from the EA Monitoring API (/id/floodAreas?_limit=5000).
2. Attribute each area to every county listed in its county field (comma-separated). Increment the county's count by 1 per area.
3. Filter: exclude counties with fewer than 3 attributed areas (insufficient data).
4. Normalise:
   GFES = round(((count − 3) / (238 − 3)) × 9 + 1)
   clamped to [1, 10]

   where count is the number of EA flood areas attributed to the county, 238 is the maximum (North Yorkshire, June 2026) and 3 is the minimum qualifying count.

Score bands

Limitations

• The GFES measures county-level flood warning area density, not the percentage of land in Flood Zone 2 or 3 (which requires geospatial polygon processing of the EA's shapefiles). Users who need Flood Zone 2/3 area percentages should use the EA's own Long Term Flood Risk service.
• Flood warning areas span county boundaries; we count a multi-county area once per county. This can slightly inflate counts for counties that share many border-zone areas.
• The index covers England only (EA jurisdiction). Scotland, Wales and Northern Ireland have separate flood risk management bodies.
• The GFES is not an insurance premium quotation and does not reflect surface water flooding, groundwater flooding, or individual property risk.

Reproduce this index

The source data is freely available, no API key required:

Apply the formula above. Gera re-fetches monthly and re-publishes updated GFES scores. The dateModified in each page's Dataset JSON-LD reflects the last real data refresh.