Northolt has almost no risk from rivers or the sea, and a real one from rain. The official river-and-sea flood zones barely touch it. About one postcode in six still rates high on at least one flood measure. Surface water accounts for the difference. The canal through town draws the attention, but it isn't the thing to worry about.
The Environment Agency puts under 1% of Northolt's postcodes in flood zone 2, the medium-probability band, and none in flood zone 3, the high-probability band. The two zones don't overlap, so zone 2 is the outer fringe beyond zone 3, and in Northolt there is no zone 3 for it to surround. For flooding from rivers and the sea alone, the map is about as clean as a West London town gets.
Surface water is a separate matter. When heavy rain lands faster than drains and soil can take it, it runs downhill and pools, and that happens far from any river. Northolt is higher in the north and lower in the south, so the water runs toward the lower ground. Surface-water risk can vary between neighbouring streets, so a clean town-wide zone map doesn't make any single house safe.
The Environment Agency's climate-adjusted map, which allows for wetter conditions in future, still puts under 1% of postcodes in its flood zones. For rivers and the sea, the forward view looks much like today's.
The surface-water picture matters most at insurance time. Insurers price on modelled risk for each address, surface water included, so a house on a street the maps flag can draw a higher premium or more questions than the clean zone map would suggest. A quote on the exact address takes ten minutes, and it tells you what the market makes of that street.
Counted across every measure, rivers, sea and surface water together, about 16% of Northolt's postcodes rate high on at least one, about 20% rate medium on at least one, and about 38% rate low on at least one. A postcode counts if any single measure flags it, which is why these shares are larger than the zone figures. That gap is the surface water.
Counting homes gives an even smaller river-and-sea figure. In the Environment Agency's rivers-and-sea mapping, the postcodes that carry any risk at all contain 143 properties. One is at high risk, none at medium, 36 at low and 23 at very low. None of the homes rated high is residential. Postcodes with no river-or-sea risk don't appear in that count.
In the modelled flood extents, none of Northolt's postcodes falls in the high-probability area, with or without defences, and under 1% fall in the low-probability area with no defences. With almost nothing in the flood extents, the question of defences hardly arises. Even where a model does show a defence, that only means one exists, and it says nothing about whether it would hold.
Northolt is a long way from the coast, and the nearest tide gauge in the national record is at Portsmouth. It measured sea level rising about 2 millimetres a year between 1962 and 2023. The figure is included here for completeness and has little bearing on a town by a canal in West London.
The Environment Agency records no historic flooding in Northolt. That is good news, but it covers only what someone recorded, and a flooded back garden after a summer storm rarely ends up in the national record.
For flooding, Northolt is one of the weaker parts of the picture. Rivers and the sea are no worry, but surface water reaches enough postcodes that buyers should look at each address individually.