Sensitivity of the coasts of Canada to sea-level rise

Abstract

An objective method is used to evaluate the sensitivity of Canadian coasts to a rise in sea level of 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 2899 NTS map sheets (1:50 000 scale) that include parts of Canada's coast. 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 moderate sensitivity (scores of 5 - 15) make up 30%, and of high sensitivity, only 3%. No large areas are susceptible to catastrophic inundation by the sea but any sea-level rise would cause an increase in the rates of change. The most sensitive region includes 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. The Pacific coast has low sensitivity overall, mainly due to a preponderance of high, rocky fiord and skerry shorelines. Areas of high sensitivity include the urbanized Fraser Delta and parts of Graham Island. 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 at 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. Due to simplifications in the methodology, numerous small areas of higher sensitivity are overlooked by the scoring system. Small- and medium-sized deltas, particularly in the Arctic, outside of regions of rapidly falling sea level, and strand plains and small salt marshes fall into this category.