Water Supply Outlook for Alberta

Bow River Basin - Water Supply Forecasts

Recorded March to September 2002 natural runoff volume in the Bow River basin ranged from below-average in the northern portion of the basin to above-average in southern areas (Table 4).

Precipitation in the headwaters of the Bow River basin ranged from below-normal to much-above-normal for the March to September period. Precipitation values in the basin ranged from 80 to 144 % of normal. The early months of the season (March, April, May and June) recorded normal to much-above normal precipitation in the basin. July was extremely dry with August and September recording below-normal to normal precipitation totals. The southern sub-basins were hit by two major storms, one in late May and one in early June, which resulted in much-above-normal precipitation being recorded for the season. Northern sub-basins (mainstem of the Bow, Spray and Cascade) recorded below-normal to normal precipitation for the season. The difference in recorded precipitation is evident in the recorded March to September 2002 volumes, with northern sub-basins recording below-normal to normal natural runoff volumes and southern sub-basins showing above-normal runoff this year (Table 4).

Despite the wide variance in precipitation within the basin, the natural volume forecasts produced for the Bow River basin were within 12.6% of recorded values, on average (Table 4). The forecasts produced for the Bow River at Calgary performed well, as the natural volume forecasts were within 4% of the recorded values, on average. The basins that received the much-above-normal precipitation (Kananaskis, Elbow and Highwood basins) resulted in the overall difference (between the forecast and recorded natural volumes) being higher for the entire basin.

Bow River at Banff

The March to September 2002 recorded natural volume for the Bow River at Banff was 948,000 dam³ or 88% of average and ranks 20th lowest on record (based on the 1912-95 data) (Table 4).

Seven monthly (February to August) natural volume forecasts were produced for Banff for the March to September period (Figure 9). All seven forecasts were higher than the recorded value and were on average, within 5.7% of the recorded March to September volume. This is evident in Figure 9, where the recorded March to September 2002 natural volume at Banff (dark blue line) was below the forecasted values (brown triangles). The recorded volume was within the probable range and greater than the reasonable minimum for six out of the seven forecasts (August forecast did not). Forecasts ranged within 3.1% to 9.2% of the recorded volumes, with four of the forecasts 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 below-normal in the headwaters of the mainstem of the Bow River while the forecast volumes assume normal precipitation for the forecast period. The precipitation in the headwater portion of the basin during July was much-below-normal and as a result, impacted the recorded runoff volumes considerably, in particular the August to September period. Recorded volume for the August to September volumes was the second lowest on record.

The closest forecast to the recorded natural volume was produced in February (3.1%) (Figure 9). The forecasts remained fairly steady throughout the forecast season (brown triangles), with minor fluctuations from month to month depending on recorded precipitation.

Lake Minnewanka Inflow

The March to September 2002 recorded natural volume for the inflow to Lake Minnewanka was 191,000 dam³ or 101% of average and ranks 47th lowest on record (based on the 1912-95 data) (Table 4).

Seven monthly (February to August) natural volume forecasts were produced for Lake Minnewanka for the March to September period (Figure 10). The first five forecasts (February-June) were lower than the recorded value and the last two forecasts produced (July and August) were higher than the recorded value. The forecasts were on average, within 6.7% of the recorded March to September volume. This is evident in Figure 10, where the recorded March to September 2002 natural volume at Lake Minnewanka (dark blue line) did not deviate much from the forecasted values (brown triangles). The recorded volume was within the probable range for six out of the seven forecasts (August forecast did not) and was greater than the reasonable minimum for all the forecasts. Forecasts ranged within 1.4% to 11.7% of the recorded volumes, with four of the forecasts within five percent of the recorded value.

The closest forecast to the recorded natural volume was produced in July (1.4%) (Figure 10). The earlier forecasts (brown triangles) remained fairly steady and rose slightly in May and July due to above-normal precipitation in the basin during April and June. Forecasts in this basin performed well this year because precipitation for the season (March to September) was near normal.

Spray River near Banff

The March to September 2002 recorded natural volume for the Spray River near Banff was 339,000 dam³ or 92% of average and ranks 31st lowest on record (based on the 1912-95 data) (Table 4).

Seven monthly (February to August) natural volume forecasts were produced for the Spray River for the March to September period (Figure 11). The first three forecasts (February, March and April) were lower than the recorded value and the last four forecasts produced (May, June, July and August) were higher than the recorded value. The forecasts were on average, within 3.9% of the recorded March to September volume. This is evident in Figure 11, where the recorded March to September 2002 natural volume for the Spray River (dark blue line) did not deviate much from the forecasted values (brown triangles). The recorded volume was within the probable range and greater than the reasonable minimum for six out of the seven forecasts (August forecast did not). Forecasts ranged within 1.6% to 7.5% of the recorded volumes, with five of the forecasts within five percent of the recorded value.

The closest forecast to the recorded natural volume was produced in May (1.6%) (Figure 11). The earlier forecasts (March and April) (brown triangles) remained fairly steady and rose slightly in May and June due to above-normal precipitation in the basin during April and May. In the forecasts in the last couple months decreased due to below-normal precipitation, particularly in July. The precipitation in the headwater portion of the basin during July was much-below-normal and as a result, impacted the recorded runoff volumes considerably, in particular the August to September period. Recorded volume for the August to September volumes was the fourth lowest on record. Forecasts in this basin performed quite well this year because precipitation for the season (March to September) was near normal.

Kananaskis River

The March to September 2002 recorded natural volume for the Kananaskis River was 484,000 dam³ or 117% of average and ranks 70th lowest on record (based on the 1912-95 data) or the 16th highest on record (Table 4).

Seven monthly (February to August) natural volume forecasts were produced for the Kananaskis River for the March to September period (Figure 12). All seven forecasts were lower than the recorded value and were on average, within 20.1% of the recorded March to September volume. This is evident in Figure 12, where the recorded March to September 2002 natural volume for the Kananaskis River (dark blue line) was above the forecasted values (brown triangles). The recorded volume was within the probable range for three of the seven forecasts and was greater than the reasonable minimum for all forecasts. Forecasts ranged within 0.2% to 32.8% of the recorded volumes, with one of the forecasts within five percent of the recorded values.

The difference between the forecast and the recorded value is attributed to the fact the actual recorded precipitation was much-above-normal in the headwaters of the basin while the forecast volumes assume normal precipitation for the forecast period. Two storm systems, one in late May and the other in early June, brought significant precipitation to the basin. As a result, the recorded natural volume tended above the probable range for the first four forecasts. Once the extreme precipitation was accounted for, the recorded volume for the last three forecasts produced (June, July and August) was within the forecast probable range and were on average within 8.4% of the forecasted values.

The closest forecast to the recorded natural volume was produced in August (0.2%) (Figure 12). The forecasts increased steadily throughout the forecast season (brown triangles) because of above-normal to much-above-normal precipitation in the basin. As a result of much-above-normal precipitation in May and June, the recorded natural runoff volume tended closer to the probable upper range than the probable forecast point for the earlier forecasts.

Bow River at Calgary

The March to September 2002 recorded natural volume for the Bow River at Calgary was 2,313,000 dam³ or 95% of average and ranks 38th lowest on record (based on the 1912-95 data) (Table 4).

Seven monthly (February to August) natural volume forecasts were produced for the Bow River at Calgary for the March to September period (Figure 13). The first three forecasts (February-April) were lower than the recorded value and the last four forecasts produced (May to August) were higher than the recorded value. The forecasts were on average, within 4.0% of the recorded March to September volume. This is evident in Figure 13, where the recorded March to September 2002 natural volume at Calgary (dark blue line) did not deviate much from the forecasted values (brown triangles). The recorded volume was within the probable range and was greater than the reasonable minimum for all seven forecasts. Forecasts ranged within 1.3% to 6.2% of the recorded volumes, with five of the forecasts within five percent of the recorded value.

The closest forecast to the recorded natural volume was produced in May (1.3%) (Figure 13). Forecasts (brown triangles) remained fairly steady throughout the season with a slight rise in the May forecast due to above-normal precipitation in the basin during April. Forecasts in this basin performed well this year because precipitation for the season (March to September) was near normal.

Elbow River

The March to September 2002 recorded natural volume for the Elbow River was 252,000 dam³ or 114% of average and ranks 58th lowest on record (based on the 1912-95 data) (Table 4).

Seven monthly (February to August) natural volume forecasts were produced for the Elbow River for the March to September period (Figure 14). The first five forecasts (February-June) were lower than the recorded value and the last two forecasts produced (July and August) were higher than the recorded value. The forecasts were on average, within 23.7% of the recorded March to September volume. This is evident in Figure 14, where the recorded March to September 2002 natural volume for the Elbow River (dark blue line) was above the forecasted values (brown triangles) for the earlier forecasts. The recorded volume was within the probable range for three of the seven forecasts and was greater than the reasonable minimum for all seven forecasts. Forecasts ranged within 5.6% to 38.8% of the recorded volumes, with none of the forecasts 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-above-normal in the headwaters of the basin while the forecast volumes assume normal precipitation for the forecast period. Two storm systems, one in late May and the other in early June, brought significant precipitation to the basin. As a result, the recorded natural volume tended above the probable range for the first three forecasts. Once the extreme precipitation was accounted for, the recorded volume for the last two forecasts produced (July and August) were on average within 6.4% of the forecasted values.

The closest forecast to the recorded natural volume was produced in August (5.6%) (Figure 14). The forecasts increased steadily throughout the forecast season (brown triangles) because of above-normal to much-above-normal precipitation in the basin, particularly in June and July as a result of much-above-normal in May and June. As a result of much-above-normal precipitation in May and June, the recorded natural runoff volume tended closer to the probable upper range than the probable forecast point for the earlier forecasts.

Highwood River

The March to September 2002 recorded natural volume for the Highwood River was 689,000 dam³ or 109% of average and ranks 56th lowest on record (based on the 1912-95 data) (Table 4).

Seven monthly (February to August) natural volume forecasts were produced for the Highwood River for the March to September period (Figure 15). The first five forecasts (February-June) were lower than the recorded value and the last two forecasts produced (July and August) were higher than the recorded value. The forecasts were on average, within 24.5% of the recorded March to September volume. This is evident in Figure 15, where the recorded March to September 2002 natural volume for the Highwood River (dark blue line) was above the forecasted values (brown triangles) for the earlier forecasts. The recorded volume was within the probable range for five of the seven forecasts and was greater than the reasonable minimum for all seven forecasts. Forecasts ranged within 1.2% to 43.9% of the recorded volumes, with one of the forecasts 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-above-normal in the headwaters of the basin while the forecast volumes assume normal precipitation for the forecast period. Two storm systems, one in late May and the other in early June, brought significant precipitation to the basin. As a result, the recorded natural volume tended above the probable range for the first two forecasts. Once the extreme precipitation was accounted for, the recorded volume for the last two forecasts produced July and August) was within the forecast probable range and were on average within 3.3% of the forecasted values.

The closest forecast to the recorded natural volume was produced in August (1.2%) (Figure 15). The forecasts increased steadily throughout the forecast season (brown triangles) because of above-normal to much-above-normal precipitation in the basin, particularly in July, as a result of much-above-normal in June. Much-above-normal precipitation in May and June resulted in the recorded natural runoff volume tending closer to the probable upper range rather than the probable forecast point for the earlier forecasts.