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Developing Annual Estimates of the Economic Consequences of Shoreline Change in the United States

Research Funded: 2004
Key Words: Shoreline Change, Economic Impacts, Natural Hazards, Coastal Geology, Sea-Level Rise

Proposed Research

Key Words: Shoreline Change, Economic Impacts, Natural Hazards, Coastal Geology, Sea-Level Rise

Shoreline change is a natural phenomenon that has potentially very large social and economic consequences. Shoreline change occurs through erosion and accretion, both of which can change the risks associated with other natural hazards such as flooding and wave damage. These hazards may result from short-term storm events, longer term movements of materials from one location to another, or even longer term changes in sea level. The causes of shoreline change can be both natural and anthropogenic or a combination of the two. The large and growing human populations in coastal settings are likely to exacerbate the economic consequences of shoreline change.

  

Estimates of the economic impacts of catastrophic events, such as hurricanes or floods, often are cited to draw attention to the problem of shoreline change, but the bases of these estimates are usually left unexamined, and they are rarely used in a way to guide societal responses to shoreline change. No estimates exist of the economic consequences of shoreline change encompassing all types of hazards. Independent estimates of the costs of shoreline change have been made, but these estimates focus on different types of hazards, in different contexts, and they employ varying time frames. No estimates are reported on a regular basis at either regional or national scales. The development of annual estimates of the economic costs of shoreline change would be a useful first step toward enabling a more reasoned consideration of the scale of societal responses.  

Our goal is to develop annual estimates of the economic consequences of shoreline change at regional and national levels. This work is important because the magnitude of economic impacts associated with shoreline changes at any specific location depends upon the economic and residential features of that location. These estimates may then be useful for conducting benefit-cost analyses to aid in the selection of management measures or in studies of the value of conducting scientific research in this area.

Narrative Report

Shoreline change is a natural phenomenon that has potentially very large social and economic consequences. Shoreline change occurs through erosion and accretion, both of which can change the risks associated with other natural hazards such as flooding and wave damage. These hazards may result from short-term storm events, longer term movements of sediments from one location to another, or even longer term changes in sea level. The causes of shoreline change can be either natural or anthropogenic or a combination of the two.

The large and growing human populations in coastal settings are likely to intensify the economic consequences of shoreline change. More than 155 million people (53 percent) of the US population now reside in coastal counties, and this number is expected to grow to 168 million over the next decade. Another 180 million people visit the US coast every year, including substantial numbers of foreign visitors. Studies have estimated that between 300,000 and 350,000 homes and buildings are located within 500 feet of the US shoreline, and another 85,000 homes are located within 60-year erosion hazard areas. As many as 1,500 homes and land may be lost to erosion each year.

Few estimates exist of the economic consequences of shoreline change that encompass all types of hazards. Independent estimates of the costs of coastal hazards have been made, but these estimates focus on different types of hazards, in different contexts, and they employ varying time frames. Estimates are not reported on a regular basis at either regional or national scales. These and other gaps in our understanding of the economic consequences of shoreline change have been identified in many studies, including the recent report of the US Commission on Ocean Policy and studies published by the National Academy of Sciences.

The development of annual estimates of the economic costs of shoreline change would be a useful first step toward enabling a more reasoned consideration of the scale of societal responses. These estimates should be made at local and regional levels and aggregated to the national level.

Estimates of the economic impacts of catastrophic events, such as hurricanes or floods, often are cited to draw attention to the problem of shoreline change, but the basis of these estimates is usually left unexamined, and they are rarely used in a way to guide societal responses to shoreline change. Rough estimates of the costs of flood hazards in many areas are available from the Federal Emergency Management Agency, which oversees the national flood insurance program. More recently, national estimates of the economic costs of coastal erosion and sea level rise have been put forward.

The risk of coastal erosion may be at least as large as the risks from flooding, and in some cases, prolonged erosion and land loss can increase vulnerability to flooding, as has been suggested in the recent flooding of New Orleans . There are two main sources of value losses from coastal erosion. One concerns the decrease in the value of coastal properties as a function of the expected number of years away from inundation. This loss is a large one, amounting to several billion dollars a year. A second cost concerns the actual loss of property, including structures, due to coastal erosion. This loss may amount to as much as half a billion dollars annually at the national level. The risks of coastal erosion are not embodied explicitly in the federal flood insurance program.

Several studies have examined the costs of sea level rise due to global climate change. Accelerated sea level rise as a consequence of climate change would lead to accelerated shoreline changes. Depending upon local conditions, sea level now may rise as much as half a meter on average over the next century. Local changes in sea level may be more or less than this average, depending upon topography and geology. Recent estimates of the cost of sea level rise incorporate assumptions of adaptation, such as the possibility of allowing structures to depreciate in anticipation of sea level rise and the options of investing in either permanent or temporary shoreline protections. These estimates amount to about half a billion dollars annually by the year 2065. These estimates do not include the costs of storm events, damages to natural areas, or losses due to erosion.

Our work involves the development of estimates of rates of shoreline change based upon recent geological transects (taken during the past 30 years) that show the changing position of the coast. These transects reflect the growing influence of sea level changes due to global warming, but they may not yet fully reflect future accelerated sea level changes. The US Geological Survey has begun to map shoreline changes using similar data, but, to date, this effort has been limited to only a portion of the Gulf of Mexico coast. We are focusing our attention on the Cape Cod shoreline, which has been ignored in recent national studies of the costs of shoreline change. We are using estimated rates of shoreline change to predict the position of the coast in the future (Fig. 1).

We have collected additional data from Cape Cod towns on the location of coastal properties, the ways in which the properties are used, and their assessed values. This information forms the basis of our estimates of the costs of shoreline change in these towns. Additional work will involve the potential incorporation of topological data, evaluating the

relationship between property assessments and market values, and simulations over varying time periods and shoreline change rates. There are several issues involved in projecting changes based on past shorelines and these include possible bias in rates depending on when the photographs were taken and changes in conditions such as sediment supply that might impact future rates of erosion. Addressing these issues will involve detailed modeling that is beyond the scope of this project, but which is recognized as a major research goal of the coastal community. We expect to compare our estimates with estimates of the cost of shoreline change using the US Geological Survey data from the Gulf of Mexico.

We are very grateful for the funding provided by donors to the WHOI Coastal Ocean Institute to sponsor our work. Leading coastal geologists at WHOI and elsewhere have called for a national science program to enhance our capacity to understand long-term shoreline change. The estimates of the costs of shoreline change at local and regional scales, such as those we are developing in our work, will help to strengthen the case for this much-needed program.

Originally published: January 25, 2004