| Résumé | The upper St. Lawrence River between Kingston, at the mouth of Lake Ontario, and Montreal, about 250 km downstream, is an important river reach, with hundreds of infrastructure assets along its shorelines. Hydroelectric dam facilities regulate the flow along that reach. In the winter, water discharge is carefully managed to promote ice coverage and limit backwater extent, and is guided by an operational ice status index (ISI). This paper describes a study to anticipate ice season length and the number of mid-winter break-ups. The study covers two key sites: Lake St. Lawrence downstream of Kingston, in the international (Canada/USA) section of the river, and Canal Beauharnois, near Montreal. An ice presence prediction method was developed based on air temperature thresholds and validated against historical ISI records. This prediction method was applied, using input data from future climate scenarios, to provide information on the effects of projected climate change on the ice cover at the key sites. The modelling of future ice presence was performed using two sets of air temperature input data (climate scenarios RCP 4.5 and 8.5) over two periods (2040-2060 and 2080-2100). The predictions indicate an ongoing reduction in the ice season length due to progressively later season starts and earlier season ends. A modest increase in the number of freeze-up/break-up cycles is possible for the 2040-2060 period |
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