Southwick sits close enough to the Channel that some flood risk is a fact of geography, but the picture across the town is mixed rather than serious. About one in forty postcodes falls inside the strictest Environment Agency river-and-sea flood zone. Roughly one in eleven carries any high risk of surface-water flooding. The climate-adjusted picture does not deteriorate. A specific-street problem, not a town-wide one.
River-and-sea flood risk sits low across most of Southwick. None of the town lies inside the intermediate river-and-sea flood zone, and about one in forty postcodes falls inside the strictest one. No historic-flood incidents are recorded at postcode level. What this means in practice: most homes sit outside the zones that automatically flag on lender and insurer risk models, and a small handful sit inside them. If your target address happens to be one of the handful, you will know because the survey will tell you and the insurance quote will confirm it.
Surface-water flooding is the more common risk here. Roughly one in eleven postcodes carries some high surface-water risk, about one in eight carries medium risk, and roughly three in ten carry some low risk. Surface water is what happens when a heavy downpour lands on ground that cannot absorb it fast enough, which coastal ground rarely does. It shows up as flooded roads, blocked drains, and gardens under a couple of inches for a few hours. Rarely destructive on its own, often the difference between a small claim and none.
The climate-adjusted picture holds up under the planning horizon this data covers. Zero percent of postcodes tip into the strictest river-and-sea flood zone under projected sea-level and rainfall change. Southwick sits on the coast, and the coast is not going to stop being the coast, but the projected mapping does not currently put more of the town at the top end of the risk scale than it already is. The shoreline management policy for most of the local postcodes is Hold The Line for the next hundred years, which means engineered defences will be maintained rather than allowed to fall back, and the nearest tide gauge at Portsmouth has recorded sea-level rise of around two millimetres a year across sixty years of record.
For insurance, the mixed picture means the standard product will cover most of Southwick without a fuss. Where a specific postcode falls into a flagged zone, insurers will either add a loading, ask for a survey, or refer the risk to the Flood Re scheme, which was set up to keep flood cover accessible for at-risk properties. Flood Re does not cover homes built since 2009, so newer builds inside the zones need market-priced cover rather than the subsidised route. If you are buying, the address-level flood check is what tells you where you sit, not the town-level picture. If you are renewing, the loading on this year's premium is what the insurer thinks of your specific street.
Three out of five is the honest verdict on flood risk. Not a town where flooding is the defining question, and not a town where you can wave the question away either. Check the address rather than the postcode district, and treat surface water as the more likely of the two problems you might actually see.