Assessing the vulnerability of coasts to sea-level rise

Coastlines around the world will be affected by rising sea level over the next several decades. In some places, the impacts will be severe as flooding, erosion, and storm surge cause damage to coastal towns and transform habitats for coastal species.

The big question for resource managers and planners: Where are the most vulnerable places? The answer will be useful for prioritizing costly mitigation efforts.

In some countries, government agencies are using a coastal sensitivity index (CSI)—based on characteristics such as rock type and slope of the coastline—to identify areas that are most likely to be affected by sea-level rise.

A new article in the Journal of Coastal Conservation reports on the first attempt to apply a CSI technique to the Australian coast.

Pamela Abuodha and Colin Woodroffe tested variations of a CSI on the shores of New South Wales, where beaches alternate with steep, rocky headlands.

They found that all variations of the index produced similar results and identified the same stretches of coastline as most sensitive. Using the simplest version of the index, which required the least amount of data, did not affect the general findings.

The indices applied by Abuodha and Woodroffe incorporated up to nine variables: (a) rock type, (b) coastal slope, (c) geomorphology, (d) mean wave height, (e) mean tidal range, (f) shoreline change, (g) relative sea-level rise, (h) shoreline exposure, and (i) barrier type.

The study focused on a 167-kilometer section of coastline, which was divided into 105 grid cells. The scientists calculated the index value for each cell, repeating the process with four different combinations of variables.

As expected, all variations of the index ranked coastal sections with rocky cliffs as least sensitive and sandy beaches with low plains or dunes behind them as most sensitive.

Adding more variables to the index did not provide any meaningful benefit; when the value for each cell—from low to very high—was indicated by color on a map the overall spatial pattern was very similar for all four CSI versions.

Because it means less data collection and analysis, this finding is good news for scientists and managers who may want to apply the index.

Abuodha and Woodroffe emphasize that their CSI reflects only physical characteristics of the coast, not human demographics or socioeconomic factors, and therefore does not indicate vulnerability of human populations.  However, according to the authors,

"The results of this study provide a framework for coastal managers and planners to prioritize efforts to enhance the resilience or consider adaptation measures in the coastal zone within a study region. Sensitivity of the coast if considered in conjunction with other social factors may be an input into broader assessments of the overall vulnerability of coasts and their communities."

--by Peter Taylor

Abuodha, P., & Woodroffe, C. (2010). Assessing vulnerability to sea-level rise using a coastal sensitivity index: a case study from southeast Australia Journal of Coastal Conservation DOI: 10.1007/s11852-010-0097-0