Water Demand and Supply in Calgary – Planning for Climate Change
Calgary is the fastest growing Canadian city. The population relies solely on the Bow and Elbow Rivers for freshwater, which is supplied by snow pack and glaciers in the Alberta Rocky Mountains. However the combination of population growth, and climate changes towards drier and warmer conditions, may overwhelm the freshwater resource. The current warming trend of approximately 1ºC over 100 years means that potentially, evapotranspiration rates could exceed precipitation. The people of Calgary are large water consumers, with a per capita use that is higher than many other North American cities, while agriculture accounts for 80% of the water use from these river systems. High-volume agricultural usage during the growing season coincides with the City of Calgary's maximum period of demand. Therefore, the current rate of consumption is most likely not sustainable, given the climate changes and population growth.
Goals:
The objectives of this study were to provide quantitative projections on the impact that future climate changes are likely to have on water resources in Calgary and to provide knowledge relevant to conservation strategies that could make the resource sustainable. This research was meant to identify the vulnerabilities to water supply in order to inform decision-making and policy development. It was conducted in partnership with the City of Calgary.
Methods:
Four historical time series data sets were assembled. The first was climate indicators, which was derived from Environment Canada's climate records. Annual temperature maximums were used to identify natural cycles and trends. Daily maximum and minimum temperatures as well as daily records of snow and rain precipitation were correlated with daily water production in the city. The second was stream-flow data, where daily rates were assessed at six different locations along the Bow and Elbow Rivers. The third was water production data, which was provided by Calgary Waterworks. Daily profiles were supplied for 1986 through 2004, and annual time series data was given for 1933 to 2003. Finally, the fourth was population statistics, including annual data for 1884 to 2003 and a civic population forecast for 2004 to 2015. NRCan used this data to project the population growth in Calgary to 2064.
Results:
Data collection and analysis has indicated that:
- The maximum temperature has been increasing at a rate of approximately 0.45ºC per 100 years, with a cycle of 64 years, while the minimum temperature has been increasing at a rate of about 1.5 ºC per 100 years, with a cycle of only 30 years. These differences indicate that different forcing mechanisms may be influencing each temperature extreme.
- The total annual flow-rate will decrease by about 5.7% over the next 90 years, and historically, the flow-rate has fluctuated up to +/-12% during the multi-decadal cycles, meaning that it could get as low as only 88% of the average.
- Water production has nearly doubled over the past 35 years, and is currently increasing at a rate of approximately 5% per year. It peaks in the summer months, but due to campaigns to decrease outdoor use, per capita daily use has declined in recent years.
- The population of Calgary will double by 2064.
Conservation strategies of 25% and 50% water conservation over the next 60 years, until 2064, were assessed. It was determined by taking into account both climate change models and population growth that 25% conservation would not be sufficient, but 50% conservation would allow the freshwater resource to be sustained. However, the projected demands may still exceed the current 1000 ML per day limit in prolonged hot and drought periods. In particular, during the summers of the low flow period predicted for the early 2060's.