Water Supply Outlook for Alberta

October 2003

North Saskatchewan River Basin - Water Supply Forecasts

Recorded March to September 2003 natural runoff volume in the North Saskatchewan River basin was below-average to average at Lake Abraham, below-averge at Edmonton, and much-below-average at Brazeau Reservoir (Table 6). Despite the low runoff this year, the natural volume forecasts produced for the North Saskatchewan River basin were within 9.4% of recorded values, on average.

Precipitation in the North Saskatchewan River basin was below-normal to much-below-normal for the March to September period. Precipitation values in the basin ranged from 66 to 96 % of normal. Most months recorded much-below-normal to below-normal precipitation with the exception of March and April, where the headwaters received above-normal precipitation. The lack of runoff from spring snowpack and summer precipitation in the plains area (between Bighorn Dam and Edmonton) is clearly evident when comparing the natural volumes as a percent of average
(Table 6).

Going into last winter, the lower elevations and plains areas of the basin were dry. Winter precipitation was very low in these areas until a large snowstorm occurred in April, resulting in precipitation for the month being up to three times normal. The snow then melted very rapidly, producing near-record high runoff volumes early in the summer. Much-below-normal summer precipitation reversed this wet trend very quickly, with July through September runoff volumes being record lows. For the runoff year (March through September), volumes in 2003 were higher than in 2002. In the mountainous Bighorn Reservoir drainage basin, initial conditions were wetter as last year volumes were slightly better than average. The snowpack gradually improved over several months to below-average to average levels. By June, near-average runoff volumes were forecasted, and that is how the year finished.

North Saskatchewan River at Bighorn Dam (Lake Abraham)

The March to September 2003 recorded natural volume for the North Saskatchewan River at Bighorn Dam was below-average to average at 2,078,000 dam3 or 98% of average and ranks 10th lowest on record (based on the 1973-90 data) (Table 6). This is slightly less volume than was recorded during the same period last year.

Seven monthly (February to August) natural volume forecasts were produced for Bighorn Dam for the March to September period. As illustrated in Figure 18, the forecasted values (brown triangles) were below the recorded March to September 2003 natural volume at Bighorn 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 six of seven forecasts (all but March) and greater than the reasonable minimum in all seven forecasts.

Initial forecasts were low due to lack of snow, but steadily increased as the snowpack improved over several months to below-average to average levels and then melted quickly. Recorded runoff volumes for the March through May 2003 period were the third highest, albeit in only 19 years of record (1973-90 data). By June the forecast was for near-normal runoff volume and this forecast held steady as the July through September recorded volume ranked sixth lowest out of 32 years on record (1973-90 data). August through September was slightly wetter and finished ninth lowest on record.

Forecasts ranged within 0.3% to 12.5% of the recorded volumes, and were on average within 25.8% of the recorded March to September volume. June's forecast was the most accurate, with four of seven forecasts within 5% of the recorded value.

Brazeau River at Brazeau Dam

The March to September 2003 recorded natural volume for the Brazeau River at Brazeau Dam was much-below-average at 1,101,000 dam3 or 77% of average and ranks eighth lowest on record (based on the 1962-90 data) (Table 6). The March to September 2003 recorded volume is slightly higher than the volume recorded over the same time period last year.

Seven monthly (February to August) natural volume forecasts were produced for Brazeau Dam for the March to September period. As illustrated in Figure 19, the forecasted values (brown triangles) were below the recorded March to September 2003 natural volume at Brazeau 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 four of seven forecasts (all but June, July and August) and greater than the reasonable minimum in five of seven forecasts (all but July and August).

Initial forecasts were low due to dry antecedent conditions and lack of snow, but increased significantly as an April snowstorm resulted in precipitation for the month being up to three times normal. The snowpack as of May 1 varied throughout the basin from below-average to above-average levels, and then melted quicker than usual resulting in another increase in the forecast in June. Recorded runoff volumes for the March through May 2003 period were the fourth highest, albeit in only 30 years of record. The forecast was adjusted downward by a large amount in August as the July through September recorded volume was a record low in 33 years of record. There were extreme variations in runoff this year, from very dry antecedent conditions entering the year, to the 4th highest volume in 30 years of record during the March through May period, to a record low July through September runoff volume.

Forecasts ranged within 6.5% to 19.9% of the recorded volumes, and were on average within 11.8% of the recorded March to September volume. February's forecast was the most accurate, with none of the seven forecasts within 5% of the recorded value.

North Saskatchewan River at Edmonton

The March to September 2003 recorded natural volume for the North Saskatchewan River at Edmonton was below-average at 5,363,000 dam3 or 91% of average and ranks 35th lowest on record (based on the 1912-95 data) (Table 6). The 2003 recorded volume is much higher than the recorded volume over the same time period last year.

Seven monthly (February to August) natural volume forecasts were produced for Edmonton for the March to September period. As illustrated in Figure 20, the forecasted values (brown triangles) were below the recorded March to September 2003 natural volume at Edmonton (dark blue line) for the first three months and above during June and July. The recorded volume was within the probable range and greater than the reasonable minimum for all seven forecasts.

Initial forecasts were low due to dry antecedent conditions and lack of snow, but increased significantly as an April snowstorm resulted in precipitation for the month being up to three times normal. The snowpack as of May 1 varied throughout the basin from below-average to above-average levels, with an especially high snowpack in plains areas of the basin between the dams and Edmonton. The snow then melted quicker than usual resulting in another 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 to 1995 data). The forecast was adjusted downward in August, as the July through September recorded volume was a record low in 33 years of record. The August through September period was only slightly wetter, as it produced the second lowest volume on record. There were extreme variations in runoff this year, from very dry antecedent conditions entering the year, to the second highest volume in 85 years of record during the March through May period, to a record low July through September runoff volume.

Forecasts ranged within 0.4% to 22% of the recorded volumes, and were on average within 11.4% of the recorded March to September volume. August's forecast was the most accurate, with two of the seven forecasts (May and August) within 5% of the recorded value. After the April storm and rapid snowmelt was accounted for, the forecasts were very accurate, on average within 4.1% of the recorded volume.


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