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Trends in the Timing and Magnitude of Canadian Floods
Cunderlik, J.M. and Ouarda, T.B.M.J. 2009. Trends in the timing and magnitude of floods in Canada. Journal of Hydrology 375: 471-480.

The authors write that "information on the timing and magnitude of floods is required in many practical applications of water resources engineering," since such data are used "for estimating design flood values required in engineering design, in operational hydropower forecasting for optimal reservoir management, in floodplain management and water infrastructure operation," while adding that "change in the timing and magnitude of hydrologic extremes may be one of the most significant consequences of climate change."

What was done
Hoping to contribute to these significant societal needs, Cunderlik and Ouarda evaluated trends in the timing and magnitude of seasonal maximum flood events across Canada, based on pertinent data obtained from 162 stations of the Reference Hydrometric Basin Network established by Environment Canada over the 30-year period 1974 to 2003.

What was learned
In spite of the supposedly unprecedented warming experienced over the period of time they studied, the Canadian researchers report that "only 10% of the analyzed stations show significant trends in the timing of snowmelt floods during the last three decades (1974-2003)," and they say these results imply that "the occurrence of snowmelt floods is shifting towards the earlier times of the year," as would be expected in a warming world. However, they note that most of the identified trends "are only weakly or medium significant results," and they add that "no significant trends were found in the timing of rainfall-dominated flood events."

With respect to flood magnitudes, the two scientists state that the trends they observed "are much more pronounced than the trends in the timing of the floods," but they say that most of these trends "had negative signs, suggesting that the magnitude of the annual maximum floods has been decreasing over the last three decades [italics added]." In addition, they found that "the level of significance was also higher in these trends compared to the level of significance of the trends in the timing of annual maximum floods."

What it means
So far, it would appear that the impact of whatever global warming may have occurred over the past few decades -- even in the supposedly more sensitive higher latitudes of the planet -- has been both mild and mixed.

Reviewed 18 November 2009