Water Supply Outlook for Alberta

Red Deer River Basin - Water Supply Forecasts

Recorded March to September 2002 natural runoff volume in the Red Deer River basin was much-below-average (Table 5). Despite the low runoff this year, the natural volume forecasts produced for the Red Deer River basin were within 15.9% of recorded values, on average.

Precipitation in the headwaters of the Red Deer River basin was below-normal to much-below-normal for the March to September period. Precipitation values in the basin ranged from 71 to 98 % of normal. Most months recorded much-below-normal to below-normal precipitation with the exception of March and September, where the headwaters received above-normal precipitation.

Red Deer River at Dickson Dam

The March to September 2002 recorded natural volume for the Red Deer River at Dickson Dam was 623,000 dam³ or 66% of average and ranks 12th lowest on record (based on the 1912-95 data) (Table 5). The 2002 recorded volume is only 4% higher than the recorded volume over the same time period last year.

Seven monthly (February to August) natural volume forecasts were produced for Dickson Dam for the March to September period (Figure 16). All seven forecasts were higher than the recorded value and were on average, within 15.8% of the recorded March to September volume. This is evident in Figure 16, where the recorded March to September 2002 natural volume at Dickson Dam (dark blue line) was below the forecasted values (brown triangles). The recorded volume was within the probable range five out of seven forecasts and greater than the reasonable minimum in all seven forecasts. Forecasts ranged within 1.5% to 27.0% of the recorded volumes, of which, only one of the forecasts was within five percent of the recorded value.

The difference between the forecast and the recorded value is attributed to the fact that the actual recorded precipitation was much-below-normal in the basin while the forecast volumes assume normal precipitation for the forecast period. This is evident as the precipitation in the headwater portion of the basin during June and July, ranged between 29 and 54 % of normal. These two months are normally the highest in terms of monthly precipitation and as a result, impacted the recorded runoff volumes considerably, particularly the July to September and August to September periods. Recorded volume for the July to September period was the sixth lowest on record while the August to September volumes were the fourth lowest on record.

All seven forecasted volumes were higher than the actual recorded value as a result of the below-normal precipitation
(Figure 16). The closest forecast to the recorded natural volume was produced in August (1.5%). The forecasts remained fairly steady throughout the first part of the forecast season, with minor fluctuations from month to month depending on recorded precipitation. The July and August 1 forecasts were lowered considerably due to the much-below-normal precipitation in the headwaters during June and July. The lack of precipitation in June and July impacted recorded natural volumes considerably as the May and June forecasts did not fall within the probable range. As a result of below-normal precipitation being recorded throughout the forecast period, the recorded natural runoff volume tended closer to the probable lower range than the probable forecast point.

Red Deer River at Red Deer

The March to September 2002 recorded natural volume for the Red Deer River at Red Deer was 756,000 dam³ or 57% of average and ranks 13th lowest on record (based on the 1912-95 data) (Table 5). The 2002 recorded volume is only 5% higher than the recorded volume over the same time period last year.

Seven monthly (February to August) natural volume forecasts were produced for Red Deer for the March to September period (Figure 17). All seven forecasts were higher than the recorded value and were on average, within 16.0% of the recorded March to September volume. This is evident in Figure 17, where the recorded March to September 2002 natural volume at Red Deer (dark blue line) was below the forecasted values (brown triangles). The recorded volume was within the probable range three out of seven forecasts and greater than the reasonable minimum in six of the seven forecasts. Forecasts ranged within 5.3% to 30.0% of the recorded volumes, of which, none of the forecasts was within ten percent of the recorded value.

The difference between the forecast and the recorded value is attributed to two factors. The actual recorded precipitation was much-below-normal in the basin while the forecast volumes assume normal precipitation for the forecast period and this, combined with the basin being extremely dry as a result of drought, impacted volumes between Dickson Dam and Red Deer. The dry June and July and the extreme dry conditions that existed resulted in recorded volume for the July to September period being the eighth lowest on record while the August to September volumes were the fourth lowest on record.

All seven forecasted volumes were higher than the actual recorded value as a result of the below-normal precipitation
(Figure 17). The closest forecast to the recorded natural volume was produced in August (5.3%). The forecasts increased slightly throughout the first part of the forecast season (due to above-normal precipitation in February and March) before dropping sharply for the July and August 1 forecasts. The lack of precipitation in June and July impacted recorded natural volumes considerably as the May, June, July and August forecasts did not fall within the probable range. As a result of below-normal precipitation being recorded throughout the forecast period, the recorded natural runoff volume tended closer to the probable lower range than the probable forecast point.