Coastal flood

Coastal flood

A storm surge pushes the sea inland and floods the site. Sea-level rise makes the same surge reach further and deeper over time. The water damages the building and stops the site, and a flooded district around a dry site can stop it too. Coastal flood prices both Property damage (% of asset value) and Business interruption (% of annual revenue).

What the map shows

• Today: the Deltares coastal flood depth for the 100-year event at 2018 sea level, on a ~90 m grid (sheet).
• Projected: one depth map per horizon. 2050 is the depth Deltares published at its single 2050 sea level, the same under every scenario. 2035 and 2080 are derived by Darwin: the published flood ladder re-flooded at the IPCC AR6 regional median sea-level rise. 2035 is single-valued; 2080 differs between the low, intermediate and high emissions settings.

How the loss is computed

The engine reads the coastal depth at each return period over the site's footprint, keeping the depth reached by the wettest 20 % of the site, plus a 500 m ring around it. The same depth-damage and restoration curves as river flood turn depth into a share of asset value and days out of operation, and the losses are integrated over return periods into an annual loss. Sea-level rise is folded into the depth, never added on top. Where FLOPROS records a coastal defence standard, the integral is cut there; elsewhere the site is read undefended. Coastal flood is tagged Built, except the surroundings disruption, which is a proposal. See Damage functions: Flood and Climate risks.

Sources

• Deltares / Microsoft Planetary Computer, Global Flood Maps v2021.06, variable inun over MERIT-DEM 90 m. CDLA-Permissive 1.0.
• IPCC AR6 sea-level projections (regional, medium confidence, median; Garner et al. 2021, Zenodo 6382554), for the derived 2035 and 2080 bands. CC BY 4.0.
• FLOPROS (Scussolini et al. 2016, NHESS), coastal protection standards. CC BY 3.0.
• JRC depth-damage curves: Huizinga, de Moel & Szewczyk (2017), EUR 28552.
• HAZUS Flood Model depth-band loss-of-use (business interruption).

Limits

• The Deltares maps carry no wave setup, no coastal protection and no subsidence beyond AR6 vertical land motion.
• The coastal defence standard covers 612 of 4,647 FLOPROS polygons, so most coastal sites are read undefended and over-read.
• The 2035 and 2080 depths are derived, not published runs. Each row says whether its sea level is published or derived.
• A horizon is never priced below today: a return period is held at its 2018 depth where a future band reads lower.