CGRG Bibliography of Canadian Geomorphology
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Author : Forbes, D.L.; Thompson, K.; Bernier, N.; Parkes, G.S.; Ketch, L.A.; Mainville, A.; and Manson, G.K.
Date : 2001.
Title : Preparing for climate change in coastal communities: How high will the water come?
Publication : St. John's 2001. Geological Association of Canada - Mineralogical Association of Canada 2001 Joint Annual Meeting / l'Association géologique du Canada - l'Association minéralogique du Canada réunion annuelle conjointe. Memorial University, St. John's, Newfoundland, May 27-30 2001.
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Abstract
A project on climate-change impacts and adaptation needs in the urban centre of Charlottetown PEI provides a case study on issues and approaches for predicting future flood levels under climate change and accelerated sea-level rise. Prerequisites for such predictions include an understanding of long-term trends in relative sea-level and vertical crustal motion, predictions of global sea-level rise associated with climate warming, knowledge of the local storm climatology and potential changes in storminess and ice climatology. Coastal stakeholders need information on future flood levels as a basis for planning adaptation strategies to minimize property damage. A multidisciplinary approach has been taken in the Charlottetown project to devise the best-possible estimates of probabilities associated with potential flood levels. Geological studies on the seabed north of PEI have documented former estuarine deposits laid down 6000 years ago in present water depths of 20 m or more. Accounting for estuarine depth, these imply a long-term mean rate of relative sea level rise <0.3 m/century (<3 mm/year). The corresponding mean rate at Charlottetown this century, based on detailed quality control on tide-gauge records dating back to 1920 and earlier, is 3.2 mm/year. Part of this trend may be attributed to geological subsidence, measured by a gravity trend of +0.7±0.7 µgal/year (1971-1980). Refinement and calibration of this signal in terms of vertical motion may be accomplished using an extended time-base and geodetic GPS measurements. To quantify the frequency of flooding at Charlottetown we have adjusted the observed annual water-level maxima for the long-term rate of relative sea-level rise over the last 80 years. The corrected sea-level maxima have then been used to estimate the return times of flooding events of a specified intensity. To allow for the possibility of climate change, which can alter the frequency of flooding through a number of influences including the intensity of winter storms, we have developed a new statistical methodology for assessing flooding risk which takes explicit account of time. Using these techniques, we can demonstrate the significant influence of a plausible increase in storminess on the probability of exceeding a given level at Charlottetown as a function of time since present. This approach can be applied anywhere with a sufficiently long tide-gauge record but the analysis is non-trivial. Quite apart from uncertainties in the prediction of warming-induced global sea-level rise, large uncertainties may also remain in the local factors that determine specific flooding probabilities in a coastal community.
Bibliography of Canadian Geomorphology