Clapton has a real flood risk, and most of it falls from the sky. Only a handful of postcodes are in the river flood zones. About a third rate high on at least one flood measure. A buyer looking at the river maps alone will come away more relaxed than the full picture justifies. The Lea is the obvious worry and the rain is the bigger one.
On the Environment Agency's river-and-sea mapping, about 4% of Clapton's postcodes fall in flood zone 3, the highest-probability band, and about 6% in flood zone 2. The two zones do not overlap: zone 2 is the medium-probability fringe outside zone 3. Together they cover a small slice of E5, most of it on the low ground towards the Lea and Hackney Marsh. The Agency records 22 past flood events here, the latest a river flood in 1947, when the channel overtopped with no raised defences in place.
Surface water is a separate problem, and it does not show up in those zones at all. It means rain that falls faster than the ground and the drains can take it, so it collects in dips, basements and the lower ends of streets regardless of how far away the river is. A street in a densely built district can flood from the road outside on a day when the Lea never rises. Put the exact address into the Environment Agency's long-term flood risk service and read the surface water result as closely as the river one.
The Agency's climate-change allowance pushes the zone share up to about 13% of postcodes. That is the modelled extent once future rainfall and river flows are added, and it shows the river zones covering more of E5 than they do today.
Insurers price each address on their own models, and in a place where surface water drives most of the risk, two flats on the same street can get different quotes. A ground-floor or basement flat on the low side of a road is a different proposition to a second-floor flat at the top of it, and the premium will show the difference.
Across every measure combined, about 35% of Clapton's postcodes rate high on at least one flood indicator, about 34% rate medium on at least one, and about 56% rate low on at least one. A postcode only needs one high measure to count, and surface water supplies most of them, so these shares run far ahead of the river zones above.
Counting homes gives a much smaller number. The Environment Agency's rivers-and-sea mapping lists 2,965 properties in the postcodes it considers at some risk: one at high risk, seven at medium, 338 at low and about 1,840 at very low. Postcodes with no river or sea risk are not listed at all, and surface water is not part of this count. One home at high risk from the river, in a district where a third of postcodes rate high on something, tells you which water to watch.
About 4% of postcodes fall inside the high-probability flood extent with no defence in the model, against less than 1% where a defence appears. A defence being in the model means something is there. It does not mean it will hold, or that the home behind it stays dry.
The nearest tide gauge in the record is at Portsmouth, where the sea rose about 2 millimetres a year between 1962 and 2023. That is the rate measured on the south coast over those years, a long way from Clapton, and the risk in E5 depends far more on the rain.
Flood risk is one of Clapton's weak points, and almost all of it comes from rain that has nowhere to go, so the river maps understate it.