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Ministry of Environment

Water Supply and Streamflow Conditions Bulletin

Issued:  September 14, 2011

Weather conditions in August and the beginning of September were more typical of summer, with the southern half of the province dominated by a series of high pressure ridges and warm, dry conditions. The strongest ridge brought record-breaking temperatures to some areas of southern BC over the past week.  Despite the drier conditions in most areas, streamflows have remained near-normal for the majority of the province, with the exception of the South Thompson region.  The cool, wet spring which carried into July has helped to offset the decline in water levels normally exhibited by BC streams at this time of year.  

Weather:
Precipitation in most of the central interior and southern BC has been below normal for August and the beginning of September.  In the Okanagan and Similkameen, precipitation for August ranged from 0% (Princeton) to 32% (Penticton) of normal.  However, these values improve over the cumulative June-August period where precipitation ranged from 57-63% of normal, and again over the 6-month period where precipitation was normal.  A similar trend is observed in Kamloops, which recorded only 1% of normal precipitation for August, 65% of normal for June-August, and 108% of normal from March to August.  In the Kootenays, August precipitation was variable, with only 8% of normal observed at Castlegar, and 91% of normal recorded at Cranbrook.  However, over the 3-month period precipitation at both stations were closer to normal at 84% and 93%, respectively, and the 6-month precipitation was slightly above normal.  On the South Coast and the southern portion of Vancouver Island, August precipitation ranged from 10-65% of normal, improving to 54-74% of normal for June-August, and above normal for March to August.  In the Peace, precipitation has been below normal for August, but above normal for both the 3 and 6-month periods.  On the Central Coast, North Coast, and north east region of the province, precipitation has been normal to above normal for all 1, 3 and 6-month cumulative periods. 

Streamflow Conditions:
Although the weather during August and the beginning of September has been primarily dry, most rivers in the province continue to be near or above normal, generally above a 5-year return period low flow.  Of the streams monitored in this analysis for low flows, there are some localized exceptions in various regions.  In the southeast, this includes the Goldstream River below Old Camp Creek, and the Kootenay River at Kootenay Crossing, which are both between a 5 and 10-year return period low flow.  In the Okanagan, Vaseux Creek above Solco Creek is also between a 5 and 10-year low flow, as is Tofino Creek on Vancouver Island.  In the South Thompson, the Eagle and Salmon Rivers have also fallen to between a 5 and 10-year low flow.  However, other streams such as the Shuswap and Adams rivers and Chase Creek are only slightly below normal for this time of year. In contrast, on the North Coast, flooding occurred on the Nass River and the Bear River near Stewart in response to a heavy rainfall event last week.    

The map of 7-day average streamflow compared to historic median for several streams in the province can be viewed here.

Drought Level and Water Supply Conditions:
The cool wet spring and generally above average streamflows at the beginning of this summer have kept streamflows near normal for most areas of southern BC, despite the warm, dry weather for the past 6 weeks.  As a result, most areas of the province are at Level 1 (Normal) for drought conditions. The one exception is the South Thompson region, which is now at Level 2 (Dry).  Information on Drought in BC is available at:  http://www.livingwatersmart.ca/drought/.

Outlook:
The strong ridge of high pressure over most of southern BC over the past 10 days is breaking down, and seasonal temperatures will return by mid-week.  The Environment Canada weather forecast for Thursday includes moderate precipitation for the central interior, and light precipitation for some areas of the southern interior.  Streams are expected to stabilize or may continue to decline into next week, depending on the location and amount of rainfall received.  The dry conditions evident in the South Thompson region may also extend to other areas, particularly in smaller creeks and rivers where summer flows are maintained by rainfall.  However, it is unlikely that widespread drought conditions will develop heading into the fall.

The Ministry encourages British Columbians to conserve water to protect water sources and help manage water demands.

The River Forecast Centre will continue to monitor conditions and will provide an update as conditions warrant.

Produced by: BC River Forecast Centre
September 14, 2011