Overview

Extreme water level along the marine coastline is a result of a combination of storm surge, tides, and ocean waves. Future projections of climate change in the marine environment indicate that rising sea level and declining sea ice will cause changes in extreme water levels, which will impact Canada's coastlines and the infrastructure in these areas. Understanding these changes is essential for developing adaptation strategies that can minimize the harmful effects that may result.

CAN-EWLAT is a science-based planning tool for climate change adaptation of coastal infrastructure related to future water-level extremes and changes in wave climate. The tool includes two main components: 1) vertical allowance and 2) wave climate. CAN-EWLAT was developed primarily for DFO Small Craft Harbours (SCH) locations, but it should prove useful for coastal planners dealing with infrastructure along Canada’s ocean coastlines.

1. Vertical allowances are recommended changes in the elevation of coastal infrastructure required to maintain the current level of flooding risk in a future scenario of sea level rise. These estimates are based on a combination of the following two elements:
   • The future projections of regional sea level rise along with the uncertainties in those projections. The uncertainty is captured by the statistical distribution (defined by the 5-percentile to 95-percentile limits) of the IPCC AR5 projections of regional sea-level change for the 21st century for the RCP2.6 (low), RCP4.5 (intermediate) and RCP8.5 (high) emission scenarios. CAN-EWLAT improves upon the IPCC AR5 projections by incorporating information on land subsidence measured with high-precision GPS instruments (James et al., 2021).
   • Historical water level records including both tides and storm surge (referred to as storm tides) at tide gauge sites. At SCH sites with no tide gauge records available, we use storm-surge model to simulate storm tides (Bernier and Thompson, 2006; Zhang and Sheng, 2013; Zhai et al, 2019). It is important to note that the vertical allowance provided by CAN-EWLAT is based on historical records and does not incorporate predicted changes in storm tides over the coming century because the current state of knowledge of future projections of storminess is limited.
      
2. Wave climate: Ocean waves are generated and developed in response to winds. Often the largest waves result from marine storms, for example, extra-tropical hurricanes propagating towards the northeast, along the North American coastline, or nor’easters, propagating from Cape Hatteras towards Newfoundland and beyond. The largest waves result from the largest winds, blowing over long fetches. North Atlantic storms are expected to experience minor changes over the next fifty years, which could result in a small change to the wave climate. However, with warming air temperatures projected over the coming century, possibly the largest change in wave climate would result from changes in sea ice in coastal areas of Canada. For example, if the Gulf of St. Lawrence has significantly less sea ice in the future, the winter wave climate would be significantly different than at present where the waves are small, or non-existent, in the winter. In this case, waves could significantly impact coastal erosion, infrastructure, and winter marine activities.