Author(s): P. F. Doyle; J. F. Ball
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Abstract: Global warming is now generally acknowledged to be having widespread impacts on many aspects of water resources including river ice covers in many countries around the world. To determine changes in ice cover regime in a region of BC where river ice cover formation in winter is normal but also problematic in some years due to mechanical breakup of ice covers in mid-winter or freeze-up at high discharges, published Water Survey of Canada data on active gauging stations in the region with more than 30 years of record were investigated to determine ice cover trends. A total of 22 stations on 18 different streams that met the four study criteria of little or no missing data over the annual ice cover period, no changes to gauge location over the period, no major disturbances in the watershed, and having some ice cover in all or nearly all winters were analysed. The 4 indicators of change in annual ice cover ultimately chosen from the readily available published streamflow data were: time from first ice to last ice, longest continuous ice cover duration, date of first ice cover, and date of last ice cover. The data for individual streams showed very weak linear regression correlations between all 4 dependent variables with time over the 30 year period from 1976 to 2005 due to the large variation in the 4 indicators from year to year. However, as a group, they showed clear regional trends: first ice to last ice cover interval is growing shorter (19 support and 1 contrary), longest continuous ice cover duration is getting shorter (22 support), first ice effect day is occurring later (19 support and 3 contrary), and last ice effect day is occurring earlier (16 support and 5 contrary). A look at the same ice cover data for 7 of these 22 stations over periods of record longer than 30 years show the same results for 3 of the 4 indicators.
Year: 2008