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Storm surge

A storm surge is an unusually high water level along the coast, where low air pressure and strong onshore wind push the sea higher than the ordinary tidal peak. When a storm surge coincides with a spring tide (the highest astronomical tide), the water can stand well above normal high tide and flood quays, cellars and low-lying buildings. For coastal properties, storm surge is the single most important source of flooding, in the same way that flooding in watercourses is inland.

The water level is measured and forecast by Kartverket through a network of water level gauges along the coast. Kartverket also calculates return values: how high the water statistically reaches during a 20-year, 200-year and 1,000-year event at each location. These levels are the basis for the safety requirements in the building technical regulations. TEK17 divides buildings into safety classes for flooding and storm surge, where important buildings must withstand a rarer and higher event than, for example, a detached garage. The hazard grows over time because of sea level rise, which lifts the whole starting point that the storm surge builds on.

In a purchase or development assessment for a coastal property, storm surge is therefore a concrete cost and risk factor. Low-lying plots may require a higher foundation wall, flood embankments, sealed cellars or raised terrain to meet the Planning and Building Act section 28-1 on sufficient safety against hazards. Damage from storm surge is covered by the statutory natural perils insurance, but insurance does not remove the physical risk, and repeated events affect both operations and value. Storm surge is also a central parameter in an overall assessment of climate risk for property portfolios. Report: Risk and climate risk takes storm surge and sea level rise together, since one builds on the other.

How the dataset appears in the map

The dataset is part of the map layer Risk:

Storm surge in Placepoint

From Placepoint's dictionary: Storm surge

More information: Kartverket: See sea level, NVE: natural hazards

Norwegian: Stormflo (elevated coastal water level from low pressure and onshore wind).

Common questions we come across

What is a storm surge?

A storm surge is an unusually high water level along the coast, caused by low air pressure and strong onshore wind that push the sea higher than the ordinary tide. Together with a spring tide, the water can stand well above normal high tide and flood low-lying buildings.

What is the difference between storm surge and flooding?

A storm surge is flooding from the sea along the coast. Flooding is inundation from watercourses, rivers and lakes inland. Both are covered by natural perils insurance, but they are mapped and forecast by different agencies.

Where do I find storm surge levels for a property?

Kartverket calculates and publishes return values for high water levels along the coast. Placepoint shows storm surge as a risk map layer over the property, so you can assess the hazard before purchase or development.

How does storm surge affect a building project?

TEK17 requires buildings to withstand a storm surge with a given return period, depending on the safety class. Low-lying plots may require a higher foundation wall, flood protection or raised terrain, which affects the project economics. The hazard increases over time because of sea level rise.