Yes, on paper Rotherhithe is about as exposed as a district can be. Almost all of it is in the highest river-and-sea flood zone. Take the defences away and most postcodes would be in the high-risk extent. Count the defences back in and the river's threat to individual homes falls to a handful. The whole peninsula lives on the strength of a wall.
The Environment Agency's river-and-sea flood zones put about 89% of Rotherhithe's postcodes in zone 3, the highest-probability band, and another 7% in zone 2, the medium-probability fringe beyond it. The district sits inside a bend of the Thames that it spent centuries digging docks into, and the map shows it.
Rain is the other source of water. Surface-water risk has no separate share of its own in the Environment Agency's figures here. It is folded into the postcode indicators that follow, alongside the river and the sea.
Looking ahead, the Environment Agency's zone with climate change allowed for takes in about 99% of the area's postcodes. That figure comes from a model with future conditions put in. It does not record anything that has happened yet.
All this reaches insurance before it reaches the doorstep. Insurers look at the zone and the postcode, and a zone 3 address here can face more questions and a higher premium than the same flat a mile inland would, whatever the defences are doing. Get an indicative buildings insurance quote on the exact address while the offer is still being negotiated, because the premium is the part of the risk you pay every year.
Across the postcodes, counting any of several flood measures including surface water, 6% of Rotherhithe's postcodes rate high on at least one, 12% medium and 31% low. Because one postcode can register on more than one measure, these shares answer a different question from the zone figures and should not be added to them.
The property count is the figure that helps most. The Environment Agency's rivers-and-sea assessment lists about 20,700 properties in the Rotherhithe postcodes that carry some risk, and places 6 of them at high risk, none at medium, 1 at low and about 19,400 at very low. Postcodes with no risk at all are left out of the list completely. For most homes, the zone and the property rating point in opposite directions.
The defences explain the gap. Modelled without defences, the high-risk flood extent takes in about 64% of Rotherhithe's postcodes. With the defences modelled in place, it takes in none. That means a defence exists in the Environment Agency's model, and it does not mean the water has agreed to stay out. The agency has 199 recorded flood events on file here, and the most recent, in January 1928, came from the main river overtopping its defences. The wall has been tested once already, and it lost.
The nearest tide gauge with a long record is at Portsmouth, where sea level rose by about 2 millimetres a year between 1962 and 2023. That is the rate measured on the south coast over those years, and it is the closest long record available for a district on the tidal Thames.
On flood risk Rotherhithe rates poorly, because nearly every address is in the top zone and the safety of all of them depends on defences holding. Buyers here are paying for flood protection to work as well as for the flat.