Welwyn Garden City has almost no river or sea flood risk and a real, patchy risk from rain. Hardly any postcodes fall in the river flood zones. About one in twelve carries a high rating on at least one flood measure once surface water is counted. No flooding is on record. Here the rain is the risk, and the river is a footnote.
In the Environment Agency's river-and-sea flood zones, a fraction of one percent of Welwyn Garden City's postcodes fall in zone 2, the medium-probability band, and none fall in zone 3, the highest-probability band. The two zones are separate bands, so the zone 2 share is the whole of the river-and-sea exposure here. The places nearby with water in their names, Digswell Water, Tewin Water and Water End, belong to the villages and estates around the town.
Surface water is the risk those zones leave out. It comes from heavy rain that the ground and the drains cannot take quickly enough, and it can reach streets nowhere near a river. It is counted in the postcode ratings below, which is why those ratings run well ahead of the flood zones.
The Environment Agency also models the zones with an allowance for climate change. On that forward look, the share of Welwyn Garden City's postcodes affected rises only slightly and stays at a fraction of one percent.
For insurance, river and sea risk here is unlikely to trouble most quotes. Surface-water risk is the variable that can, and it is judged property by property. The Environment Agency's long-term flood risk service lets anyone check surface water for an exact address, and that is the check to run on any house here with a low spot, a basement or a garden that slopes towards the door.
Across the 1,320 postcodes assessed, about 8% rate high on at least one flood measure, about 11% medium and about 33% low. Those ratings take the worst of several measures, surface water included, so a postcode only has to score on one of them to count. A third of the town shows some flood rating, almost all of it from rain, which is a different risk from the one people imagine when they hear the word.
Counted as homes and buildings, the river-and-sea picture shrinks further. The Environment Agency's mapping lists 123 properties in the six postcodes that carry any river-or-sea risk at all. It rates 7 of them at high risk, none at medium, 13 at low and 3 at very low, and 3 of the high-risk properties are homes. Postcodes with no risk are left off the list entirely. Seven buildings is a small and specific number, and the only question that matters is whether the one being viewed is among them.
On whether anything stands between the water and the house, the Environment Agency's modelled flood extents put none of Welwyn Garden City's postcodes in the high-probability extent, with or without defences, and a fraction of one percent in the low-probability extent without them. A "defended" label would only mean a defence appears in the model. Here there is next to nothing for one to defend.
The nearest tide gauge to Welwyn Garden City is at Portsmouth, where sea level rose by about 2 millimetres a year across its record from 1962 to 2023. The fact that the gauge is at Portsmouth tells you how much the sea matters to this town.
There is no recorded historic flooding anywhere in the area. That is reassuring, as far as records go, since a flood nobody wrote down leaves no entry.
Welwyn Garden City's flood risk is middling overall, close to nil from rivers and the sea and ordinary from rain. For a buyer, surface water decides it, one house at a time.