AL9 Flood Risk
In postcode district AL9 (Welwyn Hatfield), 53 of 6,630 properties (0.8%) are in areas at high or medium risk of flooding from rivers and the sea — at least a 1 in 100 chance in any year — per Environment Agency data updated 6 July 2026; that is the 1,306th highest count of 2,181 districts in England.
By bandProperties in AL9 by flood-risk band
| Risk band | Chance of flooding each year | All properties | Homes |
|---|---|---|---|
| High | 3.3% (1 in 30) or greater chance in any year | 35 | 9 |
| Medium | between 1% and 3.3% (1 in 100 to 1 in 30) chance in any year | 18 | 5 |
| Low | between 0.1% and 1% (1 in 1,000 to 1 in 100) chance in any year | 52 | 38 |
| Very low | less than 0.1% (1 in 1,000) chance in any year | 21 | 14 |
14 of the high- or medium-risk properties are homes and 15 are non-residential (shops, offices, farms, public buildings); the rest are unclassified. By share, AL9 ranks 1,074th of 2,084 districts with at least 500 properties.
Postcode sectorsWhere in AL9 the risk sits
| Sector | Properties | High | Medium | Low | Very low | High + medium share |
|---|---|---|---|---|---|---|
| AL9 5 | 1,840 | 10 | 0 | 8 | 7 | 0.5% |
| AL9 6 | 1,067 | 7 | 1 | 2 | 0 | 0.7% |
| AL9 7 | 3,723 | 18 | 17 | 42 | 14 | 0.9% |
Recorded floodsPast floods mapped near AL9
The Environment Agency has mapped flood outlines on 2 dates near AL9 since 1987; the most recent started on 9 Feb 2009.
| Started | Place / name in the record | Source of flooding | Cause |
|---|---|---|---|
| 9 Feb 2009 – 10 Feb 2009 | — | Main river | Channel capacity exceeded (no raised defences) |
| 1 Jan 1987 – 12 Dec 1987 | — 7 outlines | Main river | Channel capacity exceeded (no raised defences) |
What this page shows, and what it misses
The Environment Agency's count of properties in each postcode that sit in areas of land at very low, low, medium or high risk of flooding from rivers and the sea, allowing for flood defences and their condition, added up here by postcode district and local authority. Every property in England is counted once, so the share is of all properties in the area.
It misses: surface water (heavy rain), groundwater, sewer and reservoir flooding; Wales, Scotland and Northern Ireland; and anything about a single building. A band describes the land a property stands on, not its floor level or flood protection, so it is not a forecast for any one home. Past floods come from the EA's Recorded Flood Outlines and are placed in the postcode district whose centre is nearest (within 12 km), so a flood near a boundary can be listed under a neighbour. Older records are patchy, and a flood with no outline is not listed.
Local authorities in AL9
- Welwyn Hatfield — 6,619 properties, 52 at high or medium risk
- East Hertfordshire — 11 properties, 1 at high or medium risk
Parishes in AL9: Essendon, Hatfield, Little Berkhamsted, North Mymms.
If you live in AL9
- Check your own address on gov.uk; it also covers surface water.
- Sign up for free flood warnings by phone, text or email: gov.uk/get-flood-warnings.
- See what is in force now on flood warnings UK, and river levels. Floodline: 0345 988 1188.
- Never walk or drive through flood water: why shallow water kills.
Nearby districts
FAQQuestions people ask
Is AL9 at risk of flooding?
In postcode district AL9 (Welwyn Hatfield), 53 of 6,630 properties (0.8%) are in areas at high or medium risk of flooding from rivers and the sea — at least a 1 in 100 chance in any year — per Environment Agency data updated 6 July 2026; that is the 1,306th highest count of 2,181 districts in England.
How many homes in AL9 are at high risk of flooding?
9 homes (residential properties) in AL9 are in areas at high risk (3.3% or greater chance each year) and 5 at medium risk, out of 5,270 homes, per Environment Agency data updated 6 July 2026. This counts rivers and the sea only, not surface water.
Has AL9 flooded before?
The Environment Agency has mapped flood outlines on 2 dates near AL9 since 1987; the most recent started on 9 Feb 2009.
How do I check the flood risk for my own address in AL9?
Use the government's long-term flood risk checker (check-long-term-flood-risk.service.gov.uk): it shows rivers and the sea, surface water, reservoirs and groundwater for one address. District figures here are totals and cannot tell you about a single home.
Flood risk counts: Environment Agency, Risk of Flooding from Rivers and Sea – Postcodes in Areas at Risk and Recorded Flood Outlines, used under the Open Government Licence v3.0. © Environment Agency copyright and/or database right 2025. All rights reserved. Some features of this information are based on digital spatial data from the Centre for Ecology & Hydrology, © NERC (CEH). © Crown Copyright and Database Rights 2025 OS AC0000807064. This product is produced in part from PAF® and Multiple Residence Data, the copyright in which is owned by Royal Mail Group Limited and/or Royal Mail Group plc. All rights reserved. Licence number AC0000807064.
Local authority of each postcode: Office for National Statistics postcode lookup (May 2026), licensed under the Open Government Licence v3.0. Contains OS data © Crown copyright and database right 2026. Contains Royal Mail data © Royal Mail copyright and database right 2026. District centres and place names: postcodes.io (ONS/OS open data). Totals, ranks and grouping are Global Incident Tracker's own calculations; the Environment Agency does not endorse them.