Photo: KTo288 · CC BY-SA 3.0Heavy rain is Hounslow’s main flood risk: 8.6% of homes, against 0.3% from rivers or the sea
On the Environment Agency’s maps, which allow for flood defences, “high or medium” means at least a 1 in 100 chance of flooding from rivers or the sea in any year. Hounslow grades B− for hazard risk: #10 of 33 in London.
What stands out about Hounslow’s hazards
From the Environment Agency’s maps and records and the BGS radon atlas, below.
What Hounslow faces
Each hazard against its own yardstick; meters run from low to high on that yardstick.
Rivers and the sea
Surface water
Past floods
The River Crane
Flood warnings
Radon
Hounslow grades B− for hazard risk
Flood risk from rivers and the sea, against all UK towns.
The share of homes at high or medium risk from rivers and the sea, ranked against every UK town of 1,000 or more: fewer homes at risk is better. Towns with none at high or medium risk are ordered by their share at low risk, so they don’t all share one score. Surface water and radon aren’t graded: they are described below.
Where the water goes in Hounslow
Turn layers on and off. Blue is the risk from rivers and the sea; pink is where heavy rain collects. Both allow for flood defences.
The river and sea risk follows the River Brent, the River Crane and the River Thames. Surface-water risk is spread across the borough, in dips, underpasses and along small streams, which is why more homes are exposed to it.
0.3% of Hounslow’s homes are at high or medium risk from rivers or the sea
The Environment Agency’s national map, allowing for defences. A further 0.9% are at low risk.
Share of each UK town’s homes at high or medium risk from rivers and the sea. 35% of UK towns have none; Hounslow has more than 53% of towns.
| # | Town | People | High or med. | |
|---|---|---|---|---|
| 1 | Southwark London | 307,076 | 0% | |
| 2 | Islington London | 216,309 | 0% | |
| 3 | Camden London | 209,342 | 0% | |
| … | ||||
| 10 | Coventry West Midlands | 344,289 | 0.3% | |
| 11 | Bradford West Yorkshire | 333,968 | 0.3% | |
| 12 | Hounslow London | 286,591 | 0.3% | |
| 13 | Northampton Northamptonshire | 243,527 | 0.3% | |
| 14 | Lambeth London | 317,108 | 0.4% | |
| … | ||||
| 43 | Nottingham Nottinghamshire | 299,786 | 3.6% | |
| 44 | Kingston upon Hull East Riding of Yorkshire | 270,816 | 6.3% | |
UK towns of 201,000 to 401,000 people.
The Environment Agency’s Risk of Flooding from Rivers and Sea (NaFRA2, June 2026) counts each postcode’s homes by band; the shares weight those postcodes by Census 2021 households. The EA counts include homes built since 2021.
Heavy rain puts about 26.9 times as many Hounslow homes at risk as rivers and the sea do
Surface water is rain that falls faster than drains and the ground can take it. It is mapped separately from rivers and the sea, and it is not in the Hazard risk Grade.
About 3.7% of homes are at high risk of surface-water flooding (a 1 in 30 chance or more each year) and 4.9% at medium risk: roughly 8,950 households. A further 15% face a low risk from surface water. That is more than 89% of UK towns.
Our estimate: every address in the borough (ONS NSUL) read on the Environment Agency’s Risk of Flooding from Surface Water map (NaFRA2, 2025), each postcode’s share weighted by its Census 2021 households. Neither agency publishes a count of homes for surface water, so treat it as a guide; one street can differ from the next.
Hounslow has flooded in 4 recorded years since 1965, most of all in 2013
Every flood the Environment Agency has mapped inside Hounslow’s built-up area, newest first. The record is fullest for big river floods; small and surface-water floods are often missing.
- 2020March 2020: The sea came inUnder 1 hectare inside today’s built-up area
- 2013November 2013: River flooding recorded5 hectares inside today’s built-up area
- 19991999: River flooding recordedUnder 1 hectare inside today’s built-up area
- 1965January 1965: River flooding recorded4 hectares inside today’s built-up area
Floodwater covered 5 hectares of what is now Hounslow in 2013, the largest flood the record holds here (November).
37 of Hounslow’s households today live inside the outline of a recorded flood.
Since 2013, the largest recorded flood inside the borough covered under 1 hectare.
The River Crane at Marsh Farm: highest 0.96 m, in October 1993
The highest level each winter (October to September) at the Environment Agency’s Marsh Farm gauge (Twickenham), since 1990. The river normally runs between 0.02 m and 1.55 m here.
- 13 October 19930.96 m
- 30 October 20000.92 m
- 4 February 19900.90 m
- 23 September 19920.88 m
- 30 May 19920.85 m
- 6 November 20000.85 m
The River Crane has topped its normal range on 0 days since 1990. By its highest day, the winter of 2025–26 was the 30th-highest of the 36.
Environment Agency Hydrology API, Marsh Farm (station 3680TH), daily maximum level; the record and normal range from the EA’s stage scale. Live river levels are on GOV.UK’s Check for flooding.
No flood warning or alert is in force for Hounslow · 0 warnings in 20 years
The Environment Agency has 11 flood warning areas and 8 alert areas reaching into the borough; warnings since the service began in 2006.
None of Hounslow’s 11 flood warning areas has had a flood warning since the service began in 2006.
Show the 19 warning and alert areas
| Area | Kind | Since 2006 | Now |
|---|---|---|---|
| Tidal Thames from the River Brent to the River Crane | Warning area | 0 | None |
| Tidal Thames from the Hogarth Lane Roundabout to the River Brent | Warning area | 0 | None |
| River Crane at Southall | Warning area | 0 | None |
| River Crane at Cranford and Feltham | Warning area | 0 | None |
| River Brent in the London Boroughs of Ealing and Hounslow | Warning area | 0 | None |
| River Crane at Twickenham | Warning area | 0 | None |
| Tidal River Crane at Isleworth | Warning area | 0 | None |
| Tidal River Brent at Brentford | Warning area | 0 | None |
| Tidal Thames from the River Crane to Teddington Weir | Warning area | 0 | None |
| Tidal Thames at Chiswick | Warning area | 0 | None |
| Tidal Thames from Putney Bridge to the Hogarth Lane Roundabout | Warning area | 0 | None |
| Tidal Thames riverside from Putney Bridge to Teddington Weir | Alert area | 757 | None |
| Tidal River Crane | Alert area | 67 | None |
| River Brent from Hendon to Brentford | Alert area | 27 | None |
| Fluvial River Crane | Alert area | 22 | None |
| Tidal Thames in the boroughs of Kensington and Chelsea, Hammersmith and Fulham, Ealing and Hounslow | Alert area | 2 | None |
| Tidal Thames in the boroughs of Wandsworth and Richmond-upon-Thames | Alert area | 2 | None |
| River Ash in the Borough of Spelthorne | Alert area | 1 | None |
| Tidal River Brent | Alert area | 1 | None |
Environment Agency Historic Flood Warnings (first issues only, not updates; “flood watch” counted as an alert before 2011) and the real-time flood-monitoring API. Sign up for free warnings on GOV.UK or call Floodline, 0345 988 1188.
Hounslow is in the lowest radon band
Radon is a natural radioactive gas from the ground; long exposure raises the risk of lung cancer. The atlas gives the chance that a home in each 1 km square is above the UK action level (200 Bq/m³).
Every 1 km square over Hounslow is in the lowest band: fewer than 1 in 100 homes are expected to be above the action level.
BGS/UKHSA Indicative Atlas of Radon in Great Britain, version 3. Check an address at UKradon.org.
Flood risk in the places around Hounslow
Share of homes at high or medium and at low risk from rivers and the sea. Tap a town for its page.
| Town | People | High or medium | Low | Hazard |
|---|---|---|---|---|
| Hounslow | 286,591 | 0.3% | 0.9% | B− |
| Richmond upon Thames | 192,888 | 2% | 6.5% | C− |
| Ealing | 367,271 | 0.6% | 0.8% | C+ |
| Sunbury-on-Thames | 21,476 | 2.1% | 6% | C− |
| Ashford Common | 8,333 | under 0.1% | 37% | B |
| Stanwell | 11,728 | 0% | 0% | A |
| Ashford | 22,823 | 0.3% | 9% | B− |
| Upper Halliford | 2,337 | 0% | under 0.1% | B+ |
Sunbury-on-Thames, 4.4 miles south-west, has the most homes at risk around Hounslow (2.1% at high or medium). Stanwell and Upper Halliford have none.
Get ready for what Hounslow faces
Free warnings, what to do in a cloudburst, and what to check before you move.
- Sign up free for Environment Agency flood warnings by text, call or email.
- Floodline: 0345 988 1188, 24 hours.
- Hounslow’s warning areas include Tidal Thames from the Hogarth Lane Roundabout to the River Brent and Tidal Thames from Putney Bridge to the Hogarth Lane Roundabout.
- Surface water rises in minutes, often with no warning issued: stay out of underpasses and dips.
- Keep the gullies and drains outside your home clear of leaves.
- Report a blocked road drain to the council.
- Never walk or drive through floodwater: 30 cm of moving water can float a car.
- Move valuables, papers and medicines upstairs.
- Turn off gas, electricity and water if you’re told to.
- Check the address on GOV.UK’s long-term flood risk service: it gives rivers and sea and surface water separately.
- Ask whether the home has flooded or had a flood insurance claim; the TA6 property form asks the seller.
- Homes built before 2009 can get flood cover through Flood Re, the government-backed scheme; newer homes can’t.
What this data can and can’t tell you
- Defences are counted. Both agencies’ maps allow for flood defences and the chance they are overtopped or fail, so a town behind a defence scheme can show few homes at high risk and many at low risk.
- Surface water is our estimate. Neither agency publishes a count of homes at risk from surface water, so we read each address on the map. A flat on a hill and a basement in a dip can share a postcode.
- Past floods are what was recorded. The flood outlines come from surveys, aerial photographs and reports; many small floods, and most surface-water floods, were never mapped.
- One town, many streets. Risk is street by street. Check a specific address on GOV.UK’s long-term flood risk service before you buy or rent.
Questions about flooding and hazards in Hounslow
Does Hounslow flood?
The last flood the Environment Agency recorded inside the borough was in March 2020. 0.3% of homes are at high or medium risk from rivers and the sea on the Environment Agency’s maps, which allow for flood defences. About 8.6% of homes are at high or medium risk from surface water, when heavy rain overwhelms the drains. Hounslow grades B− for hazard risk against UK towns.
Which parts of Hounslow are at risk of flooding?
From rivers and the sea, the places the Environment Agency warns directly: Tidal Thames from the Hogarth Lane Roundabout to the River Brent, Tidal Thames from Putney Bridge to the Hogarth Lane Roundabout, Tidal Thames at Chiswick and Tidal Thames from the River Brent to the River Crane. Surface water can collect in low spots anywhere in the borough. Check a specific address on GOV.UK’s long-term flood risk service.
When did Hounslow last flood?
The recorded flood outlines inside the borough run from 1965 to 2020 (4 years); the largest was in 2013.
Is Hounslow at risk of surface water flooding?
About 3.7% of homes are at high risk and 4.9% at medium risk from surface water, against 0.3% at high or medium risk from rivers and the sea. Surface water floods come with little warning, and the agencies don’t issue warnings for them.
Is radon a problem in Hounslow?
Not by the atlas: every 1 km square over Hounslow is in the lowest band, where fewer than 1 in 100 homes are expected to be above the action level.
Are there flood warnings in Hounslow now?
No flood warning or alert was in force near Hounslow at 6 November 2026, 03:40. Live warnings are on GOV.UK’s Check for flooding service and Floodline, 0345 988 1188.
Contains Environment Agency information © Environment Agency and/or database right 2026. Contains British Geological Survey materials © UKRI 2026.
Sources: Environment Agency Risk of Flooding from Rivers and Sea, postcodes in areas at risk (June 2026); Natural Resources Wales Flood Risk Assessment Wales (May 2026); ONS Census 2021 households by postcode · Environment Agency Risk of Flooding from Surface Water (NaFRA2, 2025) and Natural Resources Wales Flood Risk Assessment Wales surface water and small watercourses, read at every address (ONS National Statistics UPRN Lookup, September 2026) and weighted by Census 2021 households by postcode · Environment Agency Recorded Flood Outlines and Natural Resources Wales historic flood map, inside the ONS 2022 built-up-area boundary · Environment Agency Hydrology API (daily maximum river level) and flood-monitoring stage scales · Environment Agency real-time flood-monitoring API · Environment Agency Historic Flood Warnings (January 2006 to June 2026) and flood warning and alert areas · BGS/UKHSA Indicative Atlas of Radon in Great Britain, version 3, by 1 km square · TownRatings grades: our own summary of the data, ranked against UK towns only. All under the Open Government Licence v3.0.
Contains public sector information licensed under the Open Government Licence v3.0. Contains HM Land Registry data © Crown copyright and database right 2026. Contains OS data © Crown copyright and database right 2026 (ONS boundaries). Northern Ireland: Source: NISRA; contains Land & Property Services data and Ordnance Survey of Northern Ireland information, © Crown copyright, licensed under the Open Government Licence v3.0. Scotland: contains National Records of Scotland data, Registers of Scotland data and SEPA data, © Crown copyright / © SEPA 2025, licensed under the Open Government Licence v3.0.