Scientific Symposium Presentation Abstracts
September 19
Dr. Stephen P. Leatherman: Increasing the Resilience of Our Coasts
More and more people are living near the coasts of the ocean, rivers, and estuaries. Coastal watershed counties already account for about 50 percent of the population. It seems that everyone wants a waterfront view, and beachfront property has become some of the most expensive real estate in the country. Small beach cottages have given way in recent decades to luxurious, multistory houses, and in South Florida, high-rise condominiums are approaching $500 million valuations. The “Gold Coast” of Florida, which runs along the southeastern coast between Palm Beach and Miami, alone has an appraised value exceeding $1.3 trillion.
At the same time, the coast is facing a number of threats. Hurricanes are a regular occurrence along the East and Gulf coasts of the United States. Over the 20th century, 167 tropical storms made landfall. Recent years have been more active than average, further increasing the likelihood of damaging storms. Along the West Coast, winter storms, made worse on occasion due to El Niño events, pound the coastline, causing significant erosion. In total, coastal erosion is affecting almost 90% of the nation’s sandy beaches, and any erosion of the beach that takes place increases the exposure of fixed structures to the impact of major storms. With all the additional buildings located right near the coastline, that the damage costs from hurricanes and winter storms has been rising should not be surprising. Nationwide, coastal erosion and coastal flooding from storm-induced surge and heavy precipitation are each estimated to be responsible for approximately $500 million of property damage each year, including loss of structures and land.
Climate change is increasingly adding to these stresses. The rise in sea level during the 20th century is estimated to have been near 0.2 meters (about 8 inches), and projections are that, as a result of thermal expansion and glacier and ice sheet melting, human-induced changes in the climate could result in a rise in global sea level of as much as 0.5 to 1 meter (about 20 to 40 inches) by 2100 or slightly later. Along a low-lying coastline, the rate of coastal erosion is typically about two orders of magnitude greater than the rate of sea level rise (SLR), so that even small changes of SLR result in significant land loss.
In addition, hurricanes are projected to become more intense to be responsible for heavier precipitation, and there are suggestions in the observations that these changes are beginning to occur. If present trends continue, it is estimated that one of four buildings located within about 150 meters (about 500 feet) of the U.S. shoreline will be destroyed as a result of coastal erosion during the next 50-75 years., and even greater loss would be expected from more intense winter and tropical storms. Around Alaska, the retreat of sea ice is further amplifying the coastal damage by allowing winter storms to pound the frozen barrier islands that have served as the home of Inuits and other indigenous groups for many millennia; so much erosion is occurring that villages are having to be relocated inland at great expense.
With climate change expected to continue through the 21st century, and sea level rise to continue for at least several centuries, the ratio of coastal retreat to sea level rise will switch from being dependent upon erosion alone to being based on the slope of the land behind the beach (e.g., inundation of the coastal plain). Coastal dunes and their vegetation as well as estuaries and wetlands, all providing important ecological services as well as shoreline protection, will be increasingly threatened. Given the low elevation of much of southern Florida, for example, the few meter rise that it is possible could occur over the next few centuries has the potential to lead to inundation and erosion reaching many tens of kilometers (miles) inland (i.e., the ratio increasing to four orders of magnitude)—with storms actually serving to tip the ocean onto the land. Clearly, growing coastal populations and concomitant beachfront development in low-lying coastal regions in the face of rising sea levels, shoreline recession, and intensifying storms has set the US on a coastal collision course.
With so many living on the coastal edge, how can society reduce the inevitable risks of living near the shore? Beach nourishment is seen by an increasing number of coastal communities as an alternative to forcing people to move from the coasts, even though many renourished beaches have lasted only a few years rather than decades; for most locations, there is no way that this strategy will work in the long-term. By contrast, the Coastal Zone Management (CZM) Program offers states an incentive to better manage beachfront development. Unfortunately, best management practices have rarely been exercised, and unless such management efforts include provisions also for building levees around especially valuable regions or facilities and for ultimate retreat from the coastline, this approach has the potential to work only for the next few decades.
With inadequate steps to ensure coastal protection being taken, most of the burden of sustaining vulnerable (and increasingly damaged) coastal communities has fallen on FEMA and its national flood insurance program. FEMA has taken an important step by providing incentives to build new structures above the projected elevation of storm surges and to strengthen existing structures against windstorm damage, but there has been no direct consideration of horizontal shoreline movement, specifically coastal erosion, nor planning to accommodate the accelerating pace of sea level rise and the likelihood of more intense storms (with their higher winds and higher storm surges). The lack of coordinated federal programs and policies is abundantly evident as the coastal building boom continues.
A national policy for shoreline management is vitally needed. Were the further effects of climate change not facing us, Florida’s program for dealing with storm impacts and coastal erosion, which has been well-tested by the high number of hurricanes in 2004 and 2005, could be replicated by others. However, with climate change ongoing and even accelerating, the contradictory, or at least divergent, approaches to beachfront management must be replaced by a coordinated policy and streamlined process to address the nations’ growing coastal hazard losses.
