Water Supply Outlook for Alberta

October 2003

Red Deer River Basin - Water Supply Forecasts

Recorded March to September 2003 natural runoff volumes in the Red Deer River basin were 98% of average (Table 5). The natural volume forecasts produced for the Red Deer River basin were within 25.4% of recorded values, on average.

The year in the Red Deer River basin was a tale of three extremes, from two previous years of drought to near-record high (2nd to 5th highest) volumes in the spring, followed by near-record low (2nd to 3rd lowest) volumes in late summer. These large changes in weather affected the accuracy of forecasts significantly.

Red Deer River at Dickson Dam

The March to September 2003 recorded natural volume for the Red Deer River at Dickson Dam was average at 926,000 dam3 or 98% of average and ranks 39th highest on record (based on the 1912-95 data) (Table 5). This is a large improvement after very low volumes in 2001 and 2002 of 62% and 66% of average, respectively.

Seven monthly (February to August) natural volume forecasts were produced for Dickson Dam for the March to September period. As illustrated in Figure 16, the forecasted values (brown triangles) were below the recorded March to September 2003 natural volume at Dickson Dam (dark blue line) for the first three months and above for the last four months. The recorded volume was within the probable range for one of seven forecasts (May) and greater than the reasonable minimum in five of seven forecasts (all but July and August).

Initial forecasts were low due to below-average snow accumulation, and extremely dry antecedent conditions after two years of drought. The forecast increased significantly in May as a result of a major snowstorm in April greatly improving the snowpack to above-average to much-above-average. April precipitation was approximately three times normal. High runoff volumes in May due to rapid snowmelt caused another significant increase in the forecast in June. Recorded runoff volumes for the March through May 2003 period were the second highest in 85 years of record (1912-95 data). Much-below-normal summer precipitation reversed this wet trend very quickly, as the July through September recorded volume was fifth lowest on record (1912-95 data) and August through September was even drier as third lowest on record, both similar to the same periods in 2002. The August forecast was lowered significantly but the near-record dry conditions thereafter left the recorded volume less than the forecast reasonable minimum.

Forecasts ranged within 9.5% to 38.8% of the recorded volumes, and were on average within 25.8% of the recorded March to September volume. August's forecast was the most accurate.

Red Deer River at Red Deer

The March to September 2003 recorded natural volume for the Red Deer River at Red Deer was average at 1,286,000 dam3 or 98% of average and ranks 36th highest on record (based on the 1912-95 data) (Table 5). This is a large improvement after very low volumes in 2001 and 2002 of 51% and 57% of average, respectively.

Seven monthly (February to August) natural volume forecasts were produced for Red Deer for the March to September period. As illustrated in Figure 17, the forecasted values (brown triangles) were below the recorded March to September 2003 natural volume at Red Deer (dark blue line) for the first three months and above for the last four months. The recorded volume was within the probable range for four of seven forecasts (all but March, June and July) and greater than the reasonable minimum for all seven forecasts.

Initial forecasts were low due to below-average snow accumulation, and extremely dry antecedent conditions after two years of drought. The forecast increased significantly in May as a result of a major snowstorm in April greatly improving the snowpack to above-average to much-above-average. April precipitation was approximately three times normal. High runoff volumes in May due to rapid snowmelt caused another significant increase in the forecast in June. Recorded runoff volumes for the March through May 2003 period were the fifth highest in 85 years of record (1912-95 data). Much-below-normal summer precipitation reversed this wet trend very quickly, as the July through September recorded volume was 7th lowest on record (1912-95 data) and August through September was even drier as second lowest on record, both similar to the same periods in 2002. The August forecast was lowered significantly.

Forecasts ranged within 1.9% to 46.6% of the recorded volumes, and were on average within 25.0% of the recorded March to September volume. August's forecast was the most accurate. Two of seven forecasts were within six percent accuracy (May and August).


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