Climate Impacts on Ice-jam Floods in a Regulated Northern River

Abstract

The Peace-Athabasca Delta (PAD) in northern Alberta is one of the world’s largest inland freshwater deltas. Beginning in the mid-1970s, a scarcity of ice-jam flooding in the lower Peace River has resulted in prolonged dry periods and considerable reduction in the area covered by lakes and ponds that provide habitat for aquatic life in the PAD. Using archived hydrometric data and in situ observations, the ice regime of the lower Peace is quantified and ice-jam flooding is shown to depend on freeze-up stage and spring flow. The former has increased as a result of flow regulation; the latter has decreased due to recent climatic trends. This has contributed to less frequent ice-jam flooding. The frequency of ice-jam floods is further explored under “present” (1961-90) and “future” (2070-99) climatic conditions. The ice season duration is likely to be reduced by 2–4 weeks, while future ice covers would be slightly thinner than they are at present. More importantly, a large part of the Peace River basin is expected to experience frequent and sustained mid-winter thaws. These events are expected to cause significant melt and depleted snowpack in the spring, leading to severe reduction in the frequency of ice-jam flooding.