Coastal risk versus vulnerability in an uncertain sea level future

Abstract

Discussions of coastal hazards commonly use terms like risk and vulnerability interchangeably, when in fact they are much different concepts. Vulnerability describes qualities of location, structural condition, past incidence of events, and the like that render an entire coast, individual communities, or even particular coastal structures likely to suffer damage and loss and associated socio-economic impacts. But they are not the events that cause disaster (like coastal storms, exceptionally high tides, or El Niþo episodes). Sea level rise and coastal storms are two phenomena especially subject to much confusion about vulnerability and risk. General predictions of future sea level rise and coastal storminess are often treated as risk factors. Apart from uncertainties in the climate and ocean models that form the basis for such predictions, forecasted rates of sea level rise really only set conditions for events like coastal storms comprising the actual hazard. Similarly, overall coastal storm histories, even compendia of actual storm tracks, just indicate the general degree of vulnerability of coasts to future storms, not the likelihood or probability of a storm landfall or even near miss (that could produce damage) in any particular year. However, if high resolution data are available to constrain hazardous, short term increases in sea level in time and space for a reach of coast, then some probabilistic determinations may be made of yearly, seasonal, or monthly risk. Equivalent risk assessments can be prepared for the probability of coastal storm impacts in any one year, assuming the same data requirements -- extra-tropical storms, occurring every year are most suited for this kind of analysis. Most coasts in the developed world have data available which are capable of resolving exceptional sea level high stands and coastal storms to hourly levels of temporal resolution and, equally critically, location. It is increasingly evident that the variability in climate and sea level has displayed a sharp upswing since the middle 1960s. This recent phase, possibly heralding a major global climate shift, is the period from which risk assessments of hazards from sea level highstands and storms should be based.