| Résumé | For over 70 years, regular measurements of ice thickness and snow depth have been taken each winter season at 12 weather stations across the Canadian Arctic. The measurements provide valuable data on seasonal ice in a variety of environments on sea and freshwater bodies. Maximum annual ice thicknesses at the Arctic stations generally show long-term decreasing trends, although all sites show substantial variation from year to year. Of the eight sites on the sea, three have landfast ice thinning rates ranging from 2.5 to 4.3 cm/decade that are significant at the 95% confidence level. The four freshwater sites have higher, and significant, thinning rates of 5 to 8 cm/decade. Cumulative freezing degree-days (CFDD) were used as a measure of the winter severity based on air temperature. The analysis shows a significant warming trend ranging from -9 to -19 freezing degree-days per year, indicating that there is less potential for ice growth. Mean annual snow depth over ice was assessed, but inter-annual variability is so large that significant trends can only be detected at one site. To complement the analysis, historical weekly ice charts were assessed for three harbours using NRC’s Canadian Arctic Shipping Risk Assessment System (CASRAS). At those sites, the number of weeks of ice presence was found to be decreasing by 0.6 to 1.6 weeks per decade. While there are trends of thinning landfast sea ice and shortening of the winter season in northern harbours, these trends are gradual and don’t merit immediate changes to approaches for design of harbour structures or marine shipping to communities in Canada’s North. |
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