Aylesbury has a modest flood risk, concentrated on its low-lying edges and decided more by rain on clay than by the river. Barely any of the town is in the highest river flood zone. About one postcode in eleven carries a high rating on some measure. A third show at least a low one. The old town keeps dry on its hill and the estates on the clay below take the wet.
In the Environment Agency's river-and-sea flood zones, about 1% of Aylesbury's postcodes are in flood zone 3, the highest-probability band, and about 7% are in flood zone 2, the medium-probability fringe beyond it. The two bands do not overlap, so the zone 2 figure is extra ground beyond zone 3. Most of the town is outside both. The River Thame runs past the north-west side and Bear Brook cuts through the middle, which is where the river risk follows.
Surface water is the more ordinary worry here. The town centre is on a low outcrop of Portland stone, and much of the lower ground and the suburbs around it are on slowly permeable Oxford Clay and Kimmeridge Clay, the kind of soil that holds water instead of absorbing it. Heavy rain on clay does not need a river nearby to reach a back garden.
Once the Environment Agency adds its allowance for climate change, the share of postcodes in a flood zone grows to about 14%. That is its modelled view of where the flood zones could reach, and it is the figure to look at for anyone planning to stay a long time.
For most of the town, cover should be routine to arrange. Homes in or near the modelled zones along Bear Brook and the Thame are where insurers ask more questions and premiums can move. An indicative insurance quote for the exact address is the quickest way to find out which side of that line a house is on.
On the wider postcode measure, which flags a postcode if it rates on any one of several flood indicators, surface water included, about 9% of Aylesbury's postcodes carry a high risk on at least one, 13% a medium risk and 33% a low risk. Those shares overlap with the river zones above and measure something different, so the two sets cannot be added together.
Counted as properties, the Environment Agency's rivers-and-sea mapping puts 122 at high risk, 198 at medium, 1,620 at low and 651 at very low, out of 5,282 properties in the 195 postcodes that carry any risk at all. Postcodes with no river or sea risk do not appear in that count. Of the high-risk properties, 101 are homes.
About 1% of postcodes are in the high-risk river extent with no defence in the model, and about the same share with one. "Defended" here means a defence appears in the Environment Agency's model, which says nothing about whether it holds back the water at a particular front door. A flood defence on a map has never yet dried out a carpet.
The nearest tide gauge to Aylesbury is in Portsmouth, where sea level rose by about 2 millimetres a year between 1962 and 2023. The gauge measures the south coast. Aylesbury's floods come from the sky and Bear Brook, and the sea is about the last thing on the list.
Aylesbury's flood risk is middling, with real exposure on the clay and along the brook and very little on the higher ground in the centre. Most buyers will never think about it, and the ones near the water should.