Dulwich has no river or sea flood risk on the official maps, and its real exposure is rain. None of it is in a river or sea flood zone. About one postcode in six rates high on at least one flood measure. The water that matters here falls from the sky and runs downhill.
The Environment Agency's river-and-sea mapping puts none of Dulwich's postcodes in flood zone 3, the highest-probability band, and none in flood zone 2, the medium-probability band that surrounds it. Those two zones measure only rivers and the sea. In Dulwich, the result is a clean sheet on both.
Surface water is a different measure, and it gives a different answer. Heavy rain that the ground and the drains can't absorb pools in low spots, and a district that sits in a valley between Crystal Palace, Sydenham Hill and Denmark Hill has plenty of low spots. Large parts of Dulwich were built on land that used to be wet. West Dulwich grew on what was once Dulwich Common, which flooded often until Edward Alleyn's estate drained it. The drainage changed what the land was used for. The slope of the valley is still there.
The Environment Agency's climate-adjusted flood zones, which allow for heavier rivers and higher seas in future, also show none of Dulwich's postcodes affected. If river and sea risk is your worry, the forward look doesn't change the picture.
Insurers don't stop at the river-and-sea zones. They price surface-water risk too, often by postcode, so a house on a street that rates high for surface water can still face a higher premium or questions about past claims, even though Dulwich is clear of the flood zones. Get an insurance quote on the exact address early, while you're still deciding, and not after the survey.
Taken postcode by postcode across Dulwich, where a postcode counts if it rates on any one of several flood measures, surface water included, about 16% of postcodes come out high on at least one, about 17% medium and about 46% low. Those shares cover rain and rivers together. That's why they look so different from the zone figures above, which are empty. "Not in a flood zone" is true for every address in Dulwich, and for one postcode in six it isn't the whole answer.
On the question of whether anything stands between the water and the houses, the Environment Agency's modelled flood extents show none of Dulwich's postcodes in a high-risk river or sea extent, defended or undefended. The model has nothing to defend against here. It doesn't model the surface water that makes up Dulwich's actual risk, and drainage isn't something these maps cover.
The nearest tide gauge in the records is at Portsmouth, where sea level rose by about 2 millimetres a year between 1962 and 2023. That's a past rate, measured on the south coast, and with no part of Dulwich in a tidal flood zone it tells you little about any house here.
The Environment Agency's historic flood records show no recorded flood outlines in Dulwich. That's reassuring for river and sea flooding. Surface-water flooding often goes unrecorded at this level, though, so a clean history means nobody mapped a flood, and that is weaker than saying none ever happened.
Dulwich's flood risk is worse than its blank flood-zone maps suggest. Rivers and the sea aren't the problem. The rain running down the valley sides is enough to make this a weak point for one postcode in six.