Lower Edmonton has a moderate flood risk. A small share of the area is in the highest-risk river-and-sea zone. About a fifth more is in the medium-risk band around it. Count surface water as well and one postcode in ten rates high on at least one measure. The rain gets a say here as well as the rivers.
About 5% of Lower Edmonton's postcodes fall in the Environment Agency's Flood Zone 3, the highest-probability band for rivers and the sea, and about 21% fall in Flood Zone 2. The two zones don't overlap: Flood Zone 2 is the medium-probability belt outside Flood Zone 3, so the bigger number is the outer band. The Environment Agency has ten flood events on record here. The most recent was in October 2000, when a main river overflowed its channel at a spot with no raised defences. The record doesn't give the river's name, only that it ran out of room.
Those zones only cover water coming out of rivers or in from the sea. Surface water from heavy rain backing up in drains and low-lying streets has no zone of its own, and it only appears in the combined postcode measure, which is why that measure comes out higher.
With the Environment Agency's climate change allowance added to the river-and-sea modelling, about 33% of postcodes would be in a flood zone. That is a modelled look at what the future might hold, and the borders would move with it.
For insurance, the zone a house is in and any flood history at the address both affect what cover costs and whether it is easy to get. A home in Flood Zone 3, or one with a past claim, may face higher premiums or a narrower choice of insurers. A home in neither usually gets cover on ordinary terms. Getting an indicative quote for the exact address, early on, is the quickest way to find out which group a house falls into.
The postcode measure takes the worst result from any of several flood sources, surface water included. On that basis, about 10% of Lower Edmonton's postcodes rate high, 22% medium and 55% low. A postcode only needs one bad rating to count.
The Environment Agency's rivers-and-sea mapping also counts individual properties. Across the 328 postcodes that carry any risk at all, 87 properties rate high risk, 76 of them homes, along with 635 at medium risk, 3,788 at low risk and 1,958 at very low risk, out of 9,716 properties in total. Postcodes with no modelled risk aren't listed at all, so that total covers only the streets with some exposure.
About 4% of postcodes fall inside the high-probability flood extent where the Environment Agency's model shows no defence, and about 1% fall inside it where a defence is shown. "Defended" only means the model includes a wall or embankment. It says nothing about how well that defence would hold.
The nearest tide gauge is at Portsmouth, where the sea rose by about 2 millimetres a year between 1962 and 2023. The nearest tide gauge being on the south coast tells you how small a part the sea plays in Lower Edmonton's flood risk.
Flood risk here is moderate. Most homes are clear of the river zones, but enough postcodes rate high, once rain is counted alongside the rivers, that it matters which street a house is on.