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There is no question that climate change during the last century has had a significant impact on winter hydrology in Ontario, Canada. On the basis of data from 13 climatological stations from across Ontario, Canada, for the last 70 years of record, time series for a number of winter temperature variables revealed steady and significant upward trends. There were no significant trends in the time series of total winter precipitation; however, winter rainfall revealed increasing trends and winter snowfall revealed decreasing trends. Correspondingly, winter rainfall as a percentage of total winter precipitation was found to have been increasing, and winter snowfall as a percentage of total winter precipitation has been decreasing. The number of rainy days during the winter months was found to be increasing, but the number of snowy days has remained unchanged. The results of this climate change study will be particularly useful for climatologists, hydrologists, environmental scientists and water resource managers who are interested in, and involved in the management of, impacts of climate change on winter hydrology.

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