Yes, and the risk is mostly rain. Rivers and the sea barely touch the town. Surface water is another matter. About a third of postcodes carry a high rating on at least one flood measure. The problem is in the drains and the low spots, not on a floodplain.
The Environment Agency's river-and-sea mapping puts about 1% of Borehamwood's postcodes in Flood Zone 3, the highest-probability band, and about 5% more in Zone 2, the medium-probability fringe beyond it. The two bands do not overlap, so together they cover a small slice of the town. On river and sea flooding alone, Borehamwood would barely rate a mention.
Those zones leave surface water out entirely, and surface water is the town's real exposure. Heavy rain on a densely built post-war town has to go somewhere, and where drains and gradients send it is a separate question from where any river goes. The postcode figures further down include it, which is why they read so differently from the zones.
With the agency's allowance for a changed climate, the river-and-sea extent grows to about 8% of postcodes. The agency models that zone to show where the edge moves if rainfall and river flows rise as projected. As forward looks go it is a modest one, and it still leaves surface water out.
For insurance, the exposure matters at the level of the individual home. Where a property's own postcode carries a surface-water rating, insurers price that. A semi a few streets from a dry one can come back with a noticeably different quote, which is why the useful check here is an indicative buildings insurance quote on the exact address while the survey is being booked, not after exchange.
Taking every measure together, surface water included, about 34% of Borehamwood's postcodes rate high on at least one flood indicator, 30% medium and 55% low. A postcode lands in a band if any one of several measures puts it there, so the shares overlap and do not add up to a hundred. They give the widest view of the risk, and they are the reason a town with almost no floodplain carries a flood warning at all.
Counted by property, the Environment Agency's rivers-and-sea mapping lists 1,023 homes and other buildings in the postcodes it flags, with 67 at high risk, 44 at medium and 392 at low. Of the high-risk properties, 63 are homes. Only postcodes with some river or sea risk appear in that count, so the rest of the town is simply missing from it. Sixty-seven is a short list, though no comfort to the people on it.
About 2% of postcodes fall inside the high-probability flood extent with defences modelled, and the share is the same, about 2%, without them. In the agency's model, whatever defences exist make no measurable difference to the high-risk footprint here. A defence in the model is a line on a map. It is no promise about the house behind it.
The nearest tide gauge in the agency's records is at Portsmouth, where sea level rose by about 2 millimetres a year between 1962 and 2023. That is the rate recorded at a harbour on the south coast, a long way from Hertfordshire. Borehamwood's water problems come from above.
No flooding is recorded across Borehamwood's postcodes in the historic flood records. That counts for something, since a town with a habit of flooding usually leaves a paper trail. It only covers what someone wrote down, and surface-water flooding on a residential street often goes unrecorded.
Flood risk is the weakest part of the Borehamwood picture. The rivers leave it alone, the rain does not, and a third of the town's postcodes carry the evidence.