by Peter Dixon
What is the extent of our understanding how climate change will impact water supplies in British Columbia? The Canadian Water Resources Association stated that the “incidence of extreme hydrological events and new and unforeseen climatic records is on the increase…” A few communities arebeginning to take notice.
For example, a report Enhancing Water Supply Infrastructure Investment Planning Practices for a Changing Climate for the Okanagan Basin (Environment Canada) articulates a deep concern on how climate change will impact water supplies.
Streams in the Okanagan Basin area are down to record levels following a drought from the summer of 2002. The Victoria Times Colonist reported that “The provincial government granted Summerland an extension of its state of emergency regarding water Wednesday.” (“Parched Okanagan Town Struggles With Water Crisis,” Times Colonist, August 14, 2003)
Another Environment Canada report, Climate Change and the Greater Vancouver Regional District, says that from April to June a 10% to 30% reduction in precipitation with no change in July and August are expected due to climate change. But in the fall, precipitation would increase 10-30% and in the winter months 10- 20%. Spring and summer are drier, fall and winter wetter. The report concludes that the GVRD temperatures have risen gradually over the last 60 to 100 years.
The long-term average estimated temperatures in the GVRD project a rise of about 3.50 C by the year 2100.
Higher temperatures in the GVRD water supply watershed will decrease the snow pack thereby reducing water stored as snow. Furthermore, since more of the precipitation will fall as rainfall during the winter and not stored as snow, water may spill over the reservoir.
The Study on Potential Rainwater and Greywater Reuse in the GVRD (Dayton & Knight Ltd.) includes climate change data from the Environment Canada climate change report and adds that per capita summer water use will still increase by 3-5% by the late 21st century.
Greater Victoria, within the Capital Regional District, is a slightly different scenario but will, nevertheless, also feel climate change.
The core municipalities are in the rain shadow from the Olympic Mountains and to a small extent from the Sooke hills. It receives less rainfall than Vancouver; hence, it is drier and subject to greater drought-like conditions.
Climate change records show temperatures rising in the Greater Victoria area. The Victoria Gonzales annual mean maximum and minimum temperatures reveal a rise in temperatures between 1899 and 2000, whereas, from 1902 to 1987 there is a downward trend in precipitation. The temperature rise is in keeping with an increase in a warming trend along the BC coast, the largest increase in any century over the past 1000 years, which is roughly the same rate as the global average.
Temperature records for the past 83 years for the Sooke Lake reservoir exhibit a rise in temperature. Yet, 107 years of records demonstrate no trends in precipitation increases or decreases at the reservoir. The ‘no trend’ agrees with longterm climate change indicators for the southern tip of Vancouver Island (Indicators of Climate Change for British Columbia 2002, Ministry of Water, Land and Air Protection). Between 1967 and 2002, weather records at the reservoir show an increase in the magnitude and frequency of dry years, which may foreshadow increases in future periodic summer droughts.
Rising temperatures combined with no increase in precipitation will necessitate an increase in irrigation of crops and gardens putting extra demand on water supply. Climate change projections – globally, provincially, and regionally – generally indicate increased warming trends and extreme precipitation events.
The evidence of climate change is increasing and, therefore, needs to be addressed at a regional level. With respect to supply and demand it should be included in water management plans.
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Peter Dixon is the president of Victoria’s Veins of Life Watershed Society
[From WS September/October 2003]