Arundel is a river town, which is another way of saying yes, parts of it flood. About one in seven of the town's postcodes sits inside Environment Agency Flood Zone 3, the highest risk band for river and sea. Roughly a quarter of postcodes carry some level of high surface-water risk. Another quarter carry medium. The Arun runs where it has always run, and the meadows do what meadows do.
River and sea flood risk is the picture the maps have carried for a long time. About one and a half per cent of the town's area sits inside Flood Zone 2, the medium-probability band. About fourteen per cent sits inside Flood Zone 3, the high-probability band. That fourteen per cent is not scattered evenly across the town: it clusters on the low ground beside the Arun, on the meadows to the south, and on the flatter ground where the river bends around the castle mound. The old town on the slope below the castle sits above most of it. Cross the bridge, drop down toward the water meadows, and you are in a different conversation with your insurer.
Surface-water flooding is the picture that catches people out, because it does not follow the river. About a quarter of postcodes here carry some level of high surface-water flood risk, another quarter carry medium risk, and roughly a third carry low. That means a substantial share of the town has some kind of pluvial exposure, most of it manageable, some of it real. Surface-water flooding is what happens when the drains cannot keep up with the sky, and old market towns with Victorian drainage systems and a lot of hard surfaces are exactly where it shows up. It is not restricted to the meadows; it can appear on streets that look fine on the river map.
The forward look is where it gets uncomfortable. With climate allowances built in, the share of the town's area falling inside a high-probability river or sea flood zone rises to about forty per cent. That is not a prediction that forty per cent of Arundel will flood; it is the modelling that says forty per cent of the town's area falls inside the zone that would be designated high-probability under mid-century sea-level and rainfall assumptions. It is the number that planning decisions, insurance underwriters and mortgage lenders are going to start referring to more, not less. Buying here without understanding it is buying without reading the small print.
Insurance is where the abstract numbers meet a monthly bill. For homes inside a Flood Zone 3 postcode, premiums are higher, excesses are higher, and some insurers will decline. Flood Re, the reinsurance scheme that puts high-risk homes into affordable cover, catches most residential properties that qualify, but Flood Re does not cover homes built since 2009. Anything modern on the low ground has to source its cover on the open market, which is where the difficult conversations happen. For an older cottage on the meadows, expect a higher premium than the town average; for a new-build on the same ground, expect a phone call that does not go well.
The verdict on flood risk is 2 out of 5, which is the honest reading of a town where about one in seven postcodes sits in the highest river-and-sea band and the climate-adjusted picture pushes that toward forty per cent of the area. Not every buyer here is buying into a flood risk, but enough of them are that the address matters more than the postcode. Read the map before you read the estate agent's brochure.