Greenford has a real flood risk, though most of it does not come from the river. Only a small share of postcodes are in the river flood zones. Count rainwater as well and about one in seven postcodes rates high on at least one measure. A few hundred properties carry a high risk from the river. The river zones are what most buyers look up, and they show the smaller part of the problem.
The Environment Agency's river-and-sea flood zones take in only a sliver of Greenford's postcodes. About 3% are in flood zone 3, the highest-probability band, and about 1% are in zone 2, the medium-probability strip just outside it. The two bands do not overlap. On the official map, most of the town is outside both.
Surface water is a separate risk, and it is what the zone map leaves out. When heavy rain falls faster than drains and soil can take it, the water collects on roads and in low gardens, well away from any river. The Environment Agency rates that risk on a separate set of maps, which is why a home outside every river zone can still carry a flood rating.
The Environment Agency also publishes a climate-adjusted version of the river-and-sea zones, which takes in about 4% of postcodes. It is a modelled scenario for a wetter future, so it tells you which streets the river is expected to reach next, not when.
Insurers price surface-water and river risk by address, so two homes a few streets apart in Greenford can get noticeably different quotes. A home in or near a high-risk band can mean a higher premium or a larger excess. Look up the exact address on the Environment Agency's long-term flood risk service, which shows surface water and rivers separately, and get an insurance quote early, while you can still walk away.
Combining every measure, surface water included, about 15% of Greenford's postcodes rate high on at least one, 23% rate medium and 46% rate low. Those shares count a postcode once whichever measure flags it. That is why they are so much higher than the river-zone figures.
Counting homes instead of postcodes, the Environment Agency's rivers-and-sea mapping lists 1,636 properties in Greenford's at-risk postcodes. Of those, 404 are at high risk, 298 at medium risk, 351 at low risk and one at very low risk. Only postcodes that carry some river or sea risk are counted. 367 of the high-risk properties are homes.
Some of that risk has defences in front of it, and some does not. In the Environment Agency's flood-extent modelling, about 3% of Greenford's postcodes fall inside the high-probability extent with no defences modelled, and about 3% with defences in place. A modelled defence lowers the odds for the homes behind it, but water can still reach them. The Environment Agency has 18 recorded flood events in the area. The latest was in December 1977, when a main river overflowed its banks where there were no raised defences.
The nearest tide gauge is at Portsmouth, where sea level rose by about 2 millimetres a year between 1962 and 2023. That is the rate measured at the coast over those years. Greenford's flood risk comes from rivers and rain, so the sea-level figure tells you very little about it.
Flood risk is one of Greenford's weaker points. The river flags only a small share of postcodes, but rainwater adds far more streets than the river zones suggest, so it is worth checking for any home you are thinking of buying.