Canadian Extreme Water Level Adaptation Tool (CAN-EWLAT)
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.
The Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR5) estimates that global mean sea level will increase quickly during the 21st century—an estimated 26 to 82 centimetres by the year 2100. From 1901 to 2010, global mean sea level rose by 19 centimetres. About 75 percent of that rise since the early 1970s has been attributed to the loss of glacier mass and thermal expansion of the oceans due to warming. Future changes in sea level will also vary regionally with some areas of Canada experiencing rates of change greater than the global average and some areas experiencing slower rates of change.
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 RCP4.5 and RCP8.5 emission scenarios. CAN-EWLAT improves upon the IPCC AR5 projections by incorporating information on land subsidence measured with high-precision GPS instruments.
- Historical water level records including both tides and storm surge (referred to as storm tides) at tide gauge sites, and storm-surge model hindcasts (Bernier and Thompson, 2006; Zhang and Sheng, 2013) at SCH sites in Atlantic Canada. 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.
For each SCH site, CAN-EWLAT will provide vertical allowance estimates from the nearest tide gauge site. In Atlantic Canada, each SCH site will also provide a local estimate based on the analysis of storm surge computer model results. In many cases, the vertical allowances from the tide gauge and computer model provide a very similar result. However, in cases where there are differences you will need to make a judgement call based on the distance to the nearest tide gauge. For example, if the SCH site is relatively close (~100 km) to the tide gauge then you should put more weight on the vertical allowance derived from the tide gauge since that is based on measured storm tides.
Important Note: For critical infrastructure, for which flooding would cause significant loss, planners should treat these models as conservative and implement vertical allowances greater than those provided by CAN-EWLAT. For these cases, we would refer the planner to a DFO technical report on 21st century mean sea level rise scenarios for Canada by Han et al. or a NOAA technical report on sea level rise scenarios by Parris et al. The choice of the high scenario from this report would provide an appropriate vertical allowance for critical infrastructure.
The vertical allowances provided on CAN-EWLAT is with respect to Mean Water Level (MWL) epoch 2010. The MWL epoch 2010 (Robin et al., 2016) relative to a known reference level including Chart Datum (CD), the North American Datum of 1983 (NAD83), the Canadian Geodetic Vertical Datum of 1928 (CGVD28), and the Canadian gravimetric geoid model of 2013 (CGG2013) are provided on the webpage for each TG and SCH site. For example, MWL_CGVD28 is defined as the height of MWL with respect to CGVD28 and, therefore, positive values indicate that MWL is above CGVD28.
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.
Bernier, N. B., and K. R. Thompson, 2006. Predicting the frequency of storm surges and extreme sea levels in the northwest Atlantic, J. Geophys. Res., 111, C10009, doi:10.1029/2005JC003168.
Han G., Z. Ma, L. Zhai, B. Greenan and R. Thomson 2016. Twenty-first century mean sea level rise scenarios for Canada. Can. Tech. Rep. Hydrogr. Ocean. Sci. 313: x + 19 pp.
Parris, A., P. Bromirski, V. Burkett, D. Cayan, M. Culver, J. Hall, R. Horton, K. Knuuti, R. Moss, J. Obeysekera, A. Sallenger, and J. Weiss, 2012. Global sea level rise scenarios for the US National Climate Assessment. NOAA Tech Memo OAR CPO-1. 37 pp.
Robin, C., S. Nudds, P. MacAulay, A. Godin, B. De Lange Boom and J. Bartlett (2016) Hydrographic Vertical Separation Surfaces (HyVSEPs) for the Tidal Waters of Canada, Marine Geodesy, 39:2, 195-222, DOI: 10.1080/01490419.2016.1160011
Zhai L., B. Greenan, J. Hunter, T.S. James, G. Han, P. MacAulay and J. Henton, 2015. Estimating sea-level allowances for Atlantic Canada using the Fifth Assessment Report of the IPCC. Atmosphere-Ocean, http://dx.doi.org/10.1080/07055900.2015.1106401.
Zhai L., B. Greenan, J. Hunter, G. Han, R. Thomson, and P. MacAulay 2014. Estimating Sea-level Allowances for the coasts of Canada and the adjacent United States using the Fifth Assessment Report of the IPCC. Can. Tech. Rep. Hydrogr. Ocean. Sci. 300: v + 146 pp.
Zhang, H., and J. Sheng, 2013, Estimation of extreme sea levels over the eastern continental shelf of North America, J. Geophys. Res. Oceans, 118, 6253–6273, doi:10.1002/2013JC009160.
If you are unfamiliar with any of the abbreviations and technical terms above, please see the Glossary of Terms.
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