Southgate is at some risk of flooding, but rivers and the sea have little to do with it. The river-and-sea flood zones hardly reach it. About a quarter of postcodes still carry a high reading once rain is counted. No flood has been recorded here. The threat comes from heavy rain, not from any river.
The Environment Agency's river-and-sea mapping puts about 1% of Southgate's postcodes in flood zone 3, the highest-probability band. Another 2% fall in flood zone 2, the medium-probability band that runs outside zone 3. The two bands don't overlap, so neither number is part of the other. On river and sea flooding alone, Southgate is close to clear.
Surface water is a separate problem, and on a place built across hills it is the one that counts. Heavy rain has to go somewhere. Roads and paving send it downhill faster than the drains can take it, and the dips along the way catch it. The 1930s estates were laid out over the hills, and every steep road among them carries water as well as cars when the rain is heavy.
The Environment Agency also models a climate-adjusted river-and-sea zone, allowing for heavier rainfall and higher flows in future. About 3% of Southgate's postcodes fall inside it. That is a small number, and it covers rivers and the sea only. The surface water above has its own model.
Insurers price on the exact property, using surface water as well as the zone. A house up on the slope and a house at the bottom of the same road can get different quotes, even with the same postcode. Get a buildings insurance quote on the specific address before you instruct a solicitor, and ask the insurer whether surface water affects the price.
Counting postcodes on any of several flood measures, surface water included, about 24% of Southgate's postcodes rate high on at least one. About 26% rate medium on at least one and about 41% low on at least one. A postcode only needs one measure to be flagged, so these are the widest of the figures here and can't be added to the zone shares above. On this count, surface water accounts for most of Southgate's high readings.
Counting homes says more than counting postcodes. The Environment Agency's rivers-and-sea mapping lists 131 properties in Southgate. Only postcodes with some risk appear in that list at all. Of those properties, 1 is at high risk and is a home, 16 are at medium risk and 65 at low. Across the whole place, one home at high risk from rivers or the sea is about as small a number as the mapping gives.
Defences make no difference to the modelled picture. About 1% of postcodes fall inside the high-probability extent with defences left out, and about 1% with them included. In that model, "defended" only means a defence exists, and it doesn't make any house safe. Here, there is little river flooding for a defence to stop. About 3% of postcodes fall inside the low-probability river-and-sea extent without defences.
The nearest tide gauge to Southgate is at Portsmouth, where sea level rose by about 2 millimetres a year across the record from 1962 to 2023. That gauge being the closest one says plenty about how far away the sea is.
The area has no recorded historic flooding. That counts in Southgate's favour, though a clean record only covers floods somebody wrote down. Water running off a road into a few gardens doesn't always end up on the Environment Agency's books.
Flood risk is one of Southgate's weaker points. The river-and-sea threat is close to nil, but surface water leaves about a quarter of its postcodes flagged high, so a buyer needs to check each house individually.