Low today, higher in the projections. River and tidal flood-zone three covers about 2% of the peninsula. No postcodes carry a historic flood record. The climate-adjusted picture puts more than a third of the area into a higher-risk zone by mid-century. Safe today, planning needed for thirty years out.
River and tidal flood-zone two covers about one in seventy-five postcodes, and the higher-probability flood-zone three covers roughly one in forty. That makes the present-day, undefended one-in-a-hundred-year flood footprint a small part of the peninsula in absolute terms. None of the postcodes carry a historic flood record in the available data, which is partly the work of the existing coastal defences and partly that Gosport's geography sits behind Portsmouth Harbour rather than facing the open Channel.
Surface-water flooding is the more present concern. Roughly one postcode in fifteen carries a high surface-water signal, about one in ten carries a moderate one, and around one in four carries a low one. Surface-water flooding is the kind that arrives in a heavy summer storm when the drains cannot keep up, not the kind that comes with a high tide. The peninsula's combination of low-lying inland creek systems, Haslar Lake, Workhouse Lake and Stoke Lake at the western end of Haslar Creek, and post-war drainage geometry means the risk is distributed unevenly. It pays to check the specific address, not just the postcode.
The forward look is the part that should weight a thirty-year mortgage decision more than today's map does. Once climate-adjusted projections are applied, flood-zone coverage jumps from a small share of the peninsula today to about 37% of it. A house safely outside the current flood zone may sit inside the climate-adjusted one, particularly along the harbour and Stokes Bay sides. Buyers planning to live in their home into the 2050s are buying tomorrow's flood map, not today's. The defences hold; the projections move.
For insurance, a property currently outside flood zone three is straightforward to cover at standard rates. A property inside the zone, or one carrying a high surface-water signal, will trigger questions from underwriters and often a higher excess on the flood element of the policy. Flood Re, the residential reinsurance scheme, can step in where a house would otherwise be uninsurable on the open market, but it does not cover homes built since 2009. Gosport's coastal protection policy is Hold The Line across the 20, 50 and 100 year horizons, which means the government has committed to defending this stretch of coast rather than letting it retreat inland. That commitment is useful for both insurance pricing and resale liquidity. It is also a policy that future budgets can revise.
Average overall: the present-day map is forgiving and the future-projected map is the one that should set the asking-price haircut. Today's risk is contained. Tomorrow's is the one to ask about before exchange.