Aug 10, 2010
Putting a price on coastal storm damage
A repeat of the 1962 Ash Wednesday "super northeaster" storm that hit North Carolina on the US East Coast would today cause structural damage with a financial impact 10 times higher. That's due to an increasing level of development on the region's coastal barrier islands, rising property values and changes to the coastline, says a team from the University of Virginia, US.
"We want to increase awareness of the potential impact of these major wintertime storms," Dave Hondula of the University of Virginia told environmentalresearchweb. "Because of the population growth in coastal communities over the past couple decades and the relative absence of super northeasters over the same time span, there may be a decreased awareness of the destructive capacity of these storms."
In the last 60 years the Outer Banks islands off North Carolina have experienced seven severe north-east storms. Two of these were "super northeasters" – the 1962 event and a Halloween storm in 1989. But due to the rapid influx of newcomers, only one-quarter of people now living in the region have ever experienced a "super northeaster".
The 1962 storm caused at least 34 deaths and damage worth $2.1 bn in today's money (more than $300 m at the time). Around 16% of all structures on the islands were either totally destroyed or badly damaged. In addition the shoreline moved inland by about 30 m and three-quarters of the protective barrier dunes were destroyed.
Part of the reason for the extensive damage was the alignment of the moon causing particularly high spring tides. But the return period for similar conditions is likely to be of the order of just 60 years.
According to the scientists, a storm like that today could cause up to $3–4 bn in losses in North Carolina alone, making it among the all-time most costly natural disasters to have occurred in the US.
"By quantifying the potential costs we hope to reach a large cross-section of those interested in coastal issues," said Hondula. Such an audience could include coastal dwellers, insurance companies and policymakers.
To come up with their cost assessment, Hondula and colleague Robert Dolan examined aerial photos of the Outer Banks taken in 1962 and 2003. They analysed damage caused by the 1962 storm and looked at how much development has occurred since then.
The damage could be classified into three zones: almost total destruction on the seaward side of the islands where the storm waves broke; moderate structural damage immediately inland because of surging and flowing water; and flood damage on the landward side of the islands caused by storm surge and overwash.
Assuming an equal number of structures in each zone, the team estimated that around 50% of the total financial losses took place in the 60 m-wide destruction zone, roughly 33% in the 150 m-wide structural damage zone, and 17% in the 300 m wide flooding zone. They then calculated the damage per structure by correcting these figures according to the actual number of structures per zone and the differing costs of damage in each zone. Finally, to estimate the costs for a storm today, the researchers multiplied the cost of damage per structure by the number of structures per zone today. They also took into account the change in property valuations.
Gradual erosion of the shoreline is exacerbating the problem by reducing the buffer between development and the sea.
"It should come as no surprise to most researchers and members of the general public that there are a large number of structures – and large amount of money – along the coast in those regions that are at greatest risk for substantial damage in major storms," said Hondula. "Our results imply that recent policies have favored coastal development in the obvious contradiction between an overall desire to protect human life and property and the appeal of coastal living."
The researchers, who reported their work in ERL, believe that their method could be easily applied, adapted and expanded to include other storms and regions.
About the author
Liz Kalaugher is editor of environmentalresearchweb.