Not from rivers or the sea, but heavy rain is a different matter. No postcode sits in the river-and-sea flood zones. There's no flooding on record. Fewer than one postcode in ten still rates high on some flood measure. The town as a whole is low risk, so the question is the specific address.
On river and sea flooding, the Environment Agency's mapping puts 0% of Petworth's postcodes in flood zone 3, the high-probability band, and 0% in flood zone 2, the medium-probability band beyond it. The two zones are separate bands, not one inside the other, and here both are empty. That's the flood type most buyers picture first, and for this town it barely applies.
Surface water is the risk that remains. It's the flooding that happens when heavy rain can't drain away fast enough, and it follows the ground, the drains and the gradient rather than a riverbank. The river-and-sea zones don't measure it at all, which is why a town with no flood-zone postcodes can still have streets that take water in a downpour. The postcode-level indicators below include it.
Looking ahead, the Environment Agency's climate-adjusted flood zone, which allows for heavier rainfall and higher river flows in future, also covers 0% of Petworth's postcodes. On the river-and-sea measure, the forward look matches the current one.
For insurance, having no postcode in a river-and-sea zone generally helps, because that's the risk most insurers price hardest. Insurers also look at surface-water ratings, though, and they rate the exact address rather than the town. Get an indicative quote on the specific property before you instruct a solicitor, not after exchange.
At postcode level, looking across every flood measure including surface water, about 8% of Petworth's postcodes are rated high risk on at least one measure. About 6% are rated medium on at least one, and about 14% low on at least one. These bands overlap with each other and with the zone figures above, so they can't be added together or read as the same thing. What they show is that the risk in Petworth is patchy and local.
On defences, the modelled high-risk flood extents cover 0% of postcodes, whether or not a defence is counted. None of the town's postcodes falls inside the model's high-risk extent, so the question of defences doesn't arise. Where a defence does appear in the model elsewhere, it only means a structure exists. It says nothing about whether a particular house stays dry.
The nearest tide gauge, at Portsmouth, recorded sea level rising by about 2 millimetres a year over its record from 1962 to 2023. That's a measured historic rate, not a forecast. For a town with no postcodes in the river-and-sea zones, it's background rather than a factor in the purchase.
Petworth has no recorded historic flooding in the area. That's reassuring. It isn't a guarantee: an event that was never recorded, or a single flooded basement, wouldn't necessarily show up in the record. Ask the seller directly and read their answer on the property information form carefully.
Petworth's flood risk is middling rather than negligible: the rivers and the sea are no threat, but a minority of postcodes carry a surface-water rating that deserves a proper check before you buy.