Arctic Freshwater Ice and Its Climatic Role

ARCTIC FRESHWATER ICE AND ITS CLIMATIC ROLE

Terry Prowse, Knut Alfredsen, Spyros Beltaos, Barrie Bonsal, Claude Duguay,Atte Korhola,
Jim McNamara, Warwick F. Vincent, Valery Vuglinsky, Gesa A. Weyhenmeyer.

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The dynamics of break-up on rivers typically generate the most important hydrological event of the year. Water levels during spring break-up often far exceed those possible under open-water conditions at equivalent levels of discharge, as shown in Fig. 1a for a station on a major tributary of the Mackenzie River (de Rham et al. 2008). For the entire Mackenzie basin, almost half (13 of 28) of the hydrometric stations were found to have annual peak water-level events occurring exclusively under ice break-up conditions. As illustrated in Fig. 1b, latitude was not found to be a major controlling factor, and other physical influences, such as elevation and slope, were considered important. However, even for sites dominated by open water, ice conditions were influential because they can significantly elevate water levels during the spring break-up period. For example, as illustrated in a dimensionless stage versus discharge plot of all station types Fig. 1c, a spring break-up flow (QI) of only 10% of the open-water flow (QO) produces a nominal water depth of at least 50% of that for open-water conditions. Within the totally ice-dominated regime of the curve, a flow equivalent to only 25% of the open-water discharge will produce an equivalent nominal water depth during spring break-up. At the extreme end, an equivalent open-water discharge will produce an approximate 50% increase in nominal water depth during the spring break-up event. This exemplifies the importance of river ice in the generation of extreme high-stage events on northern rivers. Such events can be detrimental to the built environment but are also crucial to the ecosystem health of many Arctic aquatic environments, particularly riparian zones and river deltas as described in Prowse et al. (2011 [this issue]).

REFERENCES

de Rham, L.P., T.D. Prowse, S. Beltaos and M.P. Lacroix, 2008. Assessment of annual high-water events for the Mackenzie River basin, Canada. Hydrological Processes. 22: 3864-3880.

Prowse, T.D., K. Alfredsen, S. Beltaos, B. Bonsal, W.B. Bowden, C. Duguay, A. Korhola, J. McNamara, et al. 2011. Effects of changes in arctic lake and river ice. In Arctic cryosphere - Changes and impacts, ed. Callaghan, T.V., Johansson, M. and Prowse, T.D. Ambio 40(S1).doi:10.1007/s13280-011-0217-6

Fig. 1 a) Example of a return-period plot for a station on a major tributary to the Mackenzie River, Canada, in which break-up events (triangles) become increasingly important with longer return periods in producing annual high water levels as compared to open-water events (circles); b) locations of ice (triangles), open-water (circles) and mixed (diamond) high-stage regimes in the Mackenzie River basin; and c), for these regime classifications, therelated dimensionless discharge (Q) versus water level (Y) curve for ice (I) and open-water (O) conditions. After de Rham et al. (2008).