Oldman River Basin - Water Supply Forecasts

Below-average to much-below-average natural runoff volumes are forecast for the March to September 2002 period in the Oldman River basin (Table 3a). Current forecasted values for the March to September period for the Oldman River at Lethbridge would rank 22nd lowest in 84-years of record (1912-95). The April 1 forecasts are 6 to 8 % higher than last month's forecast due to above-normal precipitation being recorded during the month of March. Current runoff volume forecasts for this year are 18 to 35% higher than recorded runoff volumes last summer.

Despite average to above-average snow accumulations at the higher elevations, below-average runoff is forecast for the March to September period because of the snow below 6000 feet is average and the extreme soil moisture deficits that exist. This year, the March to September water supply forecasts are heavily dependent on rainfall during the spring and early summer (May and June) months. Water supply from the higher elevations, given the current snow accumulations, is assured. If above-normal precipitation occurs at the lower elevations, the forecast water supply will continue to improve.

The first month of the forecast period has been completed, with March 2002 recorded runoff volumes being the much-below-average to below-average, ranging from 40 to 92 % of average. The remaining volume forecast, which is the March to September 2002 forecast minus the recorded volume to date, is available in Table 3b.