National Assessment of Coastal Vulnerability to Sea-Level Rise: Preliminary Results for the U.S. Pacific Coast

Coastal Vulnerability Index

The coastal vulnerability index (C.V.I.) presented here is similar to that used by Gornitz et al. (1994), as well as to the sensitivity index employed by Shaw et al. (1998). The index allows the six physical variables to be related in a quantifiable manner that expresses the relative vulnerability of the coast to physical changes due to sea-level rise. This method yields numerical data that cannot be equated directly with particular physical effects. It does, however, highlight those regions where the various effects of sea-level rise might be the greatest.

Once each section of coastline is assigned a risk value for each specific data variable, the coastal vulnerability index (C.V.I.) is calculated as the square root of the geometric mean of these values, or the square root of the product of the ranked variables divided by the total number of variables as

where,

• a = geomorphology
• b = coastal slope
• c = relative sea-level rise rate
• d = shoreline erosion/accretion rate
• e = mean tide range
• f = mean wave height

The C.V.I. values reported here apply specifically to the U.S. Pacific coast. Thus, absolute C.V.I. values given for other coasts (e.g., Thieler and Hammar-Klose, 1999) are not directly comparable to the data presented here. In addition to the C.V.I. values, the data ranges are also subdivided using values different from other studies so that the values used here reflect only the relative vulnerability along this coast. We feel this approach best describes and highlights the vulnerability for each of the different continental margin types that make up the U.S. coast.