hydrological.net

Severe floods caused by ice jams can have major impacts on humans as well as natural ecosystems. They can cause considerable flood damage to settlements along river banks, and can hurt aquatic biota by eroding sediment and nutrients. They are also necessary to replenish lakes and ponds in some deltas. Ice jams raise river stage by drastically increasing the roughness of the river, causing floods at lower discharges than in open water conditions. During breakup, river ice decays, fractures, is transported down river where it can jam and then eventually clear.

As climate change will cause different changes in temperature and precipitation in different regions, its affects on ice jams will vary regionally. In some areas, storms during the spring breakup are predicted to become more common, which would increase discharge and increase the risk of ice jam floods.

To examine the effects of climate change on ice jams, we will examine two rivers. In the Saint John basin, an increase in the number of mild days during winter was observed. This increases the chance of mid-winter breakups. In the Miramichi River, no significant trends in freeze up have been observed, while a significant trend in later freeze ups is occurring in the Saint John River and many other regions including Europe. Ice cover thickness also showed no significant trend in the Miramichi River, but decreases have been observed in some areas, illustrating the regional nature of climate change. Likewise, the Miramichi River has seen only a minor advance in spring breakup, while the Saint John River and most regions of Canada have seen a more significant advance. Ice jam severity is best predicted by the maximum daily flow in April. Maximum daily April flow has increased in the Miramichi River. The area has seen a cooling trend which is most significant during the spring and summer. Winter flows are increasing but have not been high enough to cause any midwinter breakups. In the Saint John River, winter flows have seen greater increases. Greater variability in flow has also been observed, as well as a warming trend.

Mid-winter breakups are common in moderate regions of Canada such as BC and the Atlantic provinces, but do not occur in colder areas. As the climate warms, these devestating events may start to occur in more places and with greater frequency.