Future Predictions for River Ice




Arctic river ice, NWT Canada

In the upcoming decades, it is predicted that there will be a northern shift of precipitation regimes. In the Arctic, this means a general increase in winter precipitation. In river systems, a higher amount of snowpack will affect the ice seasonality. In the winter, higher amounts of snow accumulation on river ice and higher temperature increases the risk for mid-season ice break-up. Additionally, in the spring, higher snowpack would increase river flow discharge and water levels. A further future scenario that may impact river systems is the thaw of permafrost. As permafrost thaws below river systems, groundwater flow surges, which would intensify base-flow of rivers. The added stress of higher precipitation and flow could alter river dynamics and increase flood risk (SWIPA, 2011).

Moreover, temperatures increases within recent decades are occurring throughout the circumpolar Arctic, which will influence trends in Arctic river ice regimes. A temperature increase in any given region will tend to delay freeze-up in the autumn and trigger ice break-up earlier in the spring. Risk of breakup ice jam flooding may be reduced in some areas, and increased in others, depending on complex interactions of local hydro climatic processes. Warmer winters would lead to an increase in mid-winter melt and related break-up of the river ice. Warmer winters would be generally expected to produce thinner ice cover and potentially reduce the persistence and severity of ice jams. In the Great Lakes and St. Lawrence basin, warmer summers would increase the amount of water evaporated from the land and from lakes. As a result of reduced runoff, water levels in the Great Lakes could fall by 0.5-1m and the amount of water flowing down the St. Lawrence River could be reduced by 20%, lowering water levels (Beltaos, 2008). Rivers in the catchment basin would be expected to experience changes to their channel shape and banks, significantly modifying the ice regime and potential positions of ice jams. Sea level rise will also affect river morphology in tidal river and estuaries: The sea-river interaction point could shift many kilometres inland, changing channel shape, bank slopes, and likely locations of ice jams.

Figure 1: Relationship between ice thickness and
discharge on a monthly basis for the Lena River, Russia
(Yang et al., 2002).

Studies on the Lena River (Siberia, Russia) suggest that increased river runoff will lead to thinner ice cover (Yang et al., 2002; Figure 1). Increased runoff from higher winter precipitation will also favour mechanical (initiated by flowing water) break-up of the river ice cover and the possibility of more severe ice jam events. Thermal (initiated by warming temperatures) river ice break-up, on the other hand, is often more gradual than mechanical break-up and results in relatively fewer ice jam events. However, delays in the fall freeze up process could actually lead to thicker ice covers, resulting in less frequent but possibly more damaging ice jams (Jepsen, et al., 2015).

For the Mackenzie River, recent research suggests that the severity of river ice break-up will be best correlated with snowpack depth at the time of melt, which directly impacts river flow (Goulding et al, 2009). This means that if snow is deeper and runoff is higher, river ice break-up is expected to be more severe on the Mackenzie in the future.



References
River Ice Links

Material on this page was provided by Thomas Bergeron and Yves Gauthier (Institut national de la recherche scientifique) and Maren Pauly and Tristan Mills (Department of Geography, University of Waterloo).