Sensitivity of the coasts of Canada to sea-level rise

GSC Bulletin 505

J. Shaw, R.B. Taylor, D.L. Forbes, M.-H. Ruz, and S. Solomon

Abstract An objective method is used to evaluate the sensitivity of Canadian coasts to a future rise in sea level of the magnitude predicted by the Intergovernmental Panel on Climate Change (IPCC).  This predicted rise is 0.65 m by the end of next century.  Based on the assumption  that the intensity of impact is related to seven quantifiable variables  - relief, geology, coastal landform, coastal retreat rate, sea-level trend, wave energy, and tidal range - a dimensionless index is determined for each of each of 2899 NTS map sheets (1: 50,000 scale) used.  Scores range from 0.8 to 57, with a mean of 5.1, and a strong mode between 2 and 4.  Areas of low sensitivity (scores below 5) constitute 67 % of the total.  Of the remainder, 30 % have moderate sensitivity (scores of 5 - 15), and only 3 % are classified as highly sensitive.  There are no large areas susceptible to catastrophic inundation by the sea.  We suggest, however, that sea-level rise would cause an intensification of rates of change. The most sensitive region is comprised of much of the coasts of Nova Scotia, Prince Edward Island and New Brunswick.  The major impacts would be higher rates of coastal erosion and retreat.  Only small parts of the coast would be permanently submerged.  Salt marshes would be subject to more frequent inundation but would accrete sufficiently to keep pace with sea-level rise.  New spits, beaches, and barriers could form in places. Many small settlements are in sensitive locations but impacts on the largest urban areas would be small.  Most of the Arctic coast has low sensitivity.  An increase in extent and duration of open water in summer would have a greater impact than sea-level rise.  On the other hand, the coast of the Beaufort Sea in the Yukon and Northwest Territories is highly sensitive.  Here anticipated impacts include more rapid coastal retreat and an acceleration in the rate in which coastal freshwater lakes are breached and converted into brackish or saline coastal embayments.  Accretion of marsh surfaces in the Beaufort Sea region may not keep pace with sea-level rise.  The Pacific coast of Canada has low sensitivity overall, mainly due to a preponderance of high, rocky fjord and skerry shorelines.  Areas of high sensitivity include the urbanised Fraser Delta and parts of Graham Island.  Due to simplifications in the methodology, numerous points of higher sensitivity throughout Canada are missed by the scoring system.  Small and medium-sized deltas fall into this category, particularly in the Arctic, outside of regions of rapidly falling sea level.  Other small areas of enhanced sensitivity include strand plains and small salt marshes.

Sensitivity of Canadian coasts to sea-level rise, from publication 24.