Markyate has a real flood risk, small in area and concentrated near the river. Only a handful of postcodes are in the river flood zones. A larger share pick up a high rating once rain running off the land is counted. A small stream that is often dry floods the village centre now and again.
The Environment Agency's river-and-sea mapping puts about 4% of Markyate's postcodes in Flood Zone 3, the highest-probability band, and about 3% more in Flood Zone 2, the medium-probability fringe outside it. Those are separate bands, so together they still cover only a small part of the village. The River Ver rises close by and runs through the centre, so that small part is the old village by the river.
Rain is the other half of the story. The Environment Agency's surface-water mapping covers water that never reaches a river at all, pooling on roads and in low gardens after heavy downpours, and in a village at the foot of rising ground that is the more likely way for a house to get wet.
With the Environment Agency's allowance for climate change applied, the share of postcodes in the flood zones rises to about 7%. That is still a small share, though it shows which way the modellers expect the river to go.
For insurance, a home in Flood Zone 3 or near the Ver can expect insurers to ask more questions and some to quote more, while most homes up the slope should notice nothing. The postcode is a starting point for an insurer and the individual house is what gets priced, so an indicative quote on the exact address tells a buyer more than any village-wide figure.
Counting every flood measure together, rivers, sea and surface water, about 16% of postcodes rate high on at least one, about 15% medium and about 33% low. Because one bad measure is enough to count, these shares run well ahead of the flood-zone figures, and they say more about rain than about the Ver.
The Environment Agency's property counts are the more useful number. Only 13 postcodes carry any river-and-sea risk at all, covering 332 properties. Of those, eight are at high risk, three of them homes, 25 at medium risk, 27 at low risk and 76 at very low risk. Eight is a short list, and the buyer's job is to find out whether the house in question is on it.
On the Environment Agency's model, about 4% of postcodes fall in the high-risk extent with defences ignored, and about 2% with defences counted. A defence in the model is a feature that changes the water's path on paper and says nothing about whether a particular house stays dry. The recorded history explains the caution: four floods are on record, the latest in December 1993, when the main river overflowed its channel with no raised defences in place.
The nearest tide gauge 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, and for a village whose flooding comes from a chalk stream and the rain, the sea is the least of its worries.
Flood risk is a weak spot for Markyate: the river zones are small, but a stream that floods the centre and a sixth of postcodes rated high on some measure are more than a buyer should wave away.