and rivers in the Northern Hemisphere, 1846-1995
(Magnuson et al., 2000).
Long-term observations of river ice freeze-up and break-up have been made for decades or even centuries for religious and cultural reasons. The longest known cryophenological record began in 1693 for River Tornionjoki (Finland). Over the last two centuries, many rives and lakes have experienced changes in their freeze-up and break-up behaviour. In general, freeze-up is occurring later in the autumn/fall, and break-up is occurring earlier in the spring (Figure 1).
As illustrated in Figure 1, the overall rate of change in the Northern Hemisphere has been a reduction of 6 days of ice per 100 years (Magnuson et al, 2000). Between 1846 and 1995, 14 of 15 records exhibit delayed freeze-up, and 24 of 24 displayed earlier spring break-up. In Canada, the Red River in Manitoba showed very significant changes: Between 1799 and 1981, the freeze-up occurred nearly 25 days later, and the break-up occurred 18 days earlier. Analysis of many river systems has shown that freeze-up and break-up dates correlate strongly (r2=0.6-0.7) with the average air temperature in the preceding autumn and spring months (Beltaos, 2008).
Material for this page was provided by Thomas Bergeron and Yves Gauthier, Institut national de la recherché scientifique.