Water Supply Outlook November 2009

Updated: November 17, 2009

Mountain runoff recorded natural volumes for March through September 2009

Natural runoff volumes recorded for the March-September 2009 period were generally below to much below average, ranking 15 to 20th lowest in 91 years of record in most areas, However, Brazeau reservoir inflow ranked among the historical lowest in 41 years of record and the Bow River at Banff and Calgary and the North Saskatchewan River at Edmonton ranked second, tenth and fourth lowest, respectively, among 91 years of record (Edmonton and Banff similar to 2001). The highest natural volumes recorded for the same period were: below average into Cascade Reservoir (29th lowest in 91 years of record) and at Milk River at Western Crossing (23rd in 70 years) and below average to average in the Elbow River at Bragg Creek (38th lowest in 91years of record).

Forecasts for these March-September volumes were accurate within 7 to 10% on average for the Bow, Oldman and North Saskatchewan River basins. Accuracies were lower for the Milk (21% difference) and Red Deer (13.3%) basins.

Milk River basin
  • March - September recorded volumes much below average except Western Crossing below to much below average
  • Seven monthly forecasts (January to August, excluding June) issued this past year for 3 locations were, on average, accurate within 14 - 27% (departure from forecast volume by location) and basin average accuracy equals 21.9% . Runoff in this basin is naturally highly variable. With low precipitation totals this year, volumes were closer to the lower end of the forecast range (lower quartile forecasts).
Oldman River basin
  • March - September recorded volumes below to much below average
  • Six monthly forecasts (February to August, excluding June) issued this past year for five locations were, on average, accurate within 3.8 - 13.8% (departure from forecast volume by location) and basin average accuracy equals 7.9%. Oldman River near Brocket had a 13.8% forecast volume departure from measured volumes; runoff was closer to the lower quartile and decile forecasts issued from February to May.
Bow River basin
  • March - September recorded volumes below to much below average, except much below average for the Bow River at Banff and Calgary, below average for the Cascade Reservoir, and below average to average for the Elbow River
  • Six monthly forecasts (February to August, excluding June) issued this past year on average ranged in accuracy from 0.8 - 14.4% for 7 locations and basin average accuracy equals 7.7%. Bow River at Banff had a 14.4% difference between forecast volume and measured volumes; runoff was closer to the lower quartile and decile forecasts due to low precipitation totals.
Red Deer River basin
  • March - September recorded volumes below to much below average
  • Six monthly forecasts (February to August, excluding June) issued this past year were, on average, accurate within 12.2 and 14.4% for Dickson Dam and Red Deer, respectively, and basin average accuracy equals 13.3% . Recent updates to preliminary volume data accounts for nearly 5 of the 14.4% error at Red Deer. Otherwise, volumes were closer to the February-May lower quartile forecasts.
North Saskatchewan River basin
  • March - September recorded volumes much below average; lowest on record (41 years) for Brazeau Reservoir, 4th lowest in 91 years for Edmonton, but below to much below average (7th lowest in 30 years) for Bighorn Reservoir
  • Six monthly forecasts (February to August, excluding June) issued this past year on average ranged in accuracy from 3.7 - 15.5% for the 3 locations and basin average accuracy equals 10.4% . Volumes were closer to the lower quartile and decile forecasts due to low precipitation totals.

Precipitation can have a major impact on water supply during the year. The forecasts above include normal precipitation into the future. The range of possible precipitation scenarios is large however, and as a result, probable range forecasts and a minimal precipitation forecast of natural runoff volume are also provided each month for each individual basin. Since more information becomes known over time, March-September volume forecast ranges will narrow.

Recorded 2009 volumes are preliminary and subject to change.

Check our Forecaster's Comments for updated information regarding runoff conditions.

Precipitation

Contoured maps of precipitation amounts and as a percent of normal for the past month and for current and recent seasons are available here. Maps of precipitation amounts for the most recent day, week and month to date are available here.

Soil Moisture

Alberta Agriculture models soil moisture for non-mountainous, agricultural areas of Alberta. Modelled soil moisture compared to average as of November 5, 2009 is available here.

Long Lead Precipitation Outlooks

Environment Canada (issued on November 1, 2009): temperature and precipitation for the November 2009 through January 2010 period:

  • below normal precipitation, except normal in northeastern Alberta.
  • normal temperatures, except below normal in the Rocky mountains and along the northern border of Alberta

National Oceanic and Atmospheric Administration (NOAA) (issued on October 15, 2009): below normal precipitation and above normal temperature for southern Alberta for November 2009 through January 2010.

Climate indicators: The NOAA reported on November 5, 2009 that El Nino conditions are expected to strengthen and last through the coming winter. Above average temperatures and below average snowfall is most likely for the Northern Rockies and Plains.

Note that forecasting weather for such a long time period into the future is very difficult, and so the historical accuracy has been variable, dependent on location and time period, and is often low, more so for precipitation than temperature. Environment Canada provides an assessment of their forecast method's historical accuracy on their website.

Reservoir storage

Water storage volumes in the major irrigation and hydroelectric reservoirs of the Milk, Oldman, Bow, Red Deer North Saskatchewan, and Athabasca River basins is updated each weekday and is available in the Provincial Reservoir Storage Summary.

Questions

Background information on the Water Supply Outlook is available in Frequently Asked Questions

Media Contact:
Communications Division, Alberta Environment
Phone: (780) 427-6267