Mountain Water Supply Forecast Summary

July precipitation in the mountains and foothills of Alberta generally ranged from 20 to 60% of normal. In addition, similarly low precipitation was measured during the last half of June. As a result, natural runoff volumes measured in July generally ranged from much below average to below to much below average, ranking among the 10th to 25th lowest in up to 91 years of record, except for Banff (2nd), Cascade Reservoir (3rd), Spray Reservoir (8th), Edmonton (4th) and the Brazeau Reservoir (2nd lowest in 41 years of data) (Table 1). Inflows to the Bighorn Reservoir were average.

Natural runoff volumes so far this year (March through July 2006) have also been much below average at Banff, Edmonton, and the Brazeau Reservoir, and below to much below average in the Red Deer River basin and at the Cascade Reservoir. However, they have been below average in the Milk River basin and most of the rest of the Bow River basin (except average to above average at the Spray Reservoir), average in most of the Oldman River basin, and above average at the Bighorn Reservoir.

For August through September 2006, natural runoff volumes are forecast to be average into the Waterton and Bighorn Reservoirs, below average to average in the remainder of the Oldman River basin, the Elbow River, and into the Spray Lakes Reservoir, below average in the Milk River basin and the rest of the Bow River basin, and below to much below average in the Red Deer River basin and the rest of the North Saskatchewan River basin.

Total natural runoff volumes for the water year (March to September 2006) are expected to range from below average to average in the Oldman River basin, below average in the Bow and Milk River basins, below to much below average in the Red Deer River basin, and much below average in the North Saskatchewan River basin (Table 1a).

Water Survey of Canada has updated their runoff volume data for 2005. Natural volumes for 2005, calculated using this data, is available in (Table 2). This 2005 data is referenced in the March - September 2006 forecast tables of this report.

Future precipitation could have an impact on water supply forecasts between now and the end of September. Streamflow volume forecasts will be updated monthly until September. Check our Forecaster's Comments throughout the month for updated information regarding runoff conditions.