Quantification of increased storm surge risk to property as sea level rises

Sea level is rising as the world ocean warms and ice caps and glaciers melt. Published estimates based on data from satellite altimeters, beginning in 1992, suggest that global mean sea level has been rising on the order of 3 mm/year. Local processes, including ocean currents and land motions due to a variety of causes, modulate the global signal spatially and temporally.

Even small increases in sea level can amplify the already devasting losses that occur when a hurricane driven storm surge coincides with an astronomical high tide. To quantify the sensitivity of property risk to increasing sea level we have calculated the percentage change in expected annual losses to property along the U.S. Gulf and East Coasts. First, we extrapolate observed trends in sea level rise from tide gauges to the year 2030, and interpolate these changes to all coastal locations. Then we use a 10,000 year catalogue of simulated hurricanes to define critical wind parameters for each event. These wind parameters, combined with a specification of the astronomical tide, then drive a parametric time-evolving storm surge model that accounts for bathymetry, coastal geometry, and surface roughness. The impact of the maximum storm surge depth on a comprehensive inventory of commercial and residential property is then calculated, using engineering models that take into account construction type.

Average annual losses projected to the year 2030 are normalized by aggregate property value on a zip code by zip code basis. Comparisons to the results of a control run reflecting the risk today quantify the change in risk per dollar of property on a percentage basis. Increases in expected losses, due to the effect of sea level rise alone, are discussed for different regions. Further sensitivity tests quantify the impact on risk of sea level rise plus additional factors, such as changes in hurricane intensity as a result of rising sea surface temperatures.