Economic Analysis of Climate Change Vulnerability and Adaptation of the Water Supply Systems of the CMQ

In Quebec, 70% of the population draws its water from surface water (rivers, lakes and the St. Lawrence River). Although these sources are abundant in Quebec, this water is not distributed equally throughout the province or over the course of the year.

Particularly hot, dry summers can cause severe low water levels that threaten the ability of some municipalities to supply their population at the very time when the demand for drinking water is greatest. The summers of 2002 and 2010 in the Québec City region are convincing examples of the potential impact of lower river water levels and the vulnerability of drinking water supply systems.

Although the marked drop in flows in the rivers of the greater Québec City metropolitan area, and in particular in the Saint-Charles River, ultimately did not cause a water shortage, it raised many questions about the long-term strategic planning of water resources for this region.

• Identify and analyze the vulnerability of potable water supply systems and the risks of water shortages.

• Perform an economic assessment of the impacts of shortages of potable water for various uses, identify relevant adaptation measures to address these impacts and evaluate their economic viability through cost-benefit analysis.

This analysis has three main steps:

1.  Climate change is integrated into the analysis and projection of river flows. To do this, the statistical analysis of hydroclimatic series is carried out for the rivers for which this data is available. This step makes it possible to project river flows on a daily basis over the time period studied.

2. Changes in the climate are integrated into the analysis and projection of the quantity of drinking water needed to meet the needs of the population. Statistical analyses of historical consumption allow the sensitivity of drinking water needs to climatic conditions to be established and extrapolated into the future. Based on population growth, combined with other factors in addition to climate change that cause consumption to vary, future needs are projected over the time period studied, again on a daily basis.

3. River flows and the quantity of water required are compared in order to identify vulnerabilities, based on several criteria, including the capacity of the current infrastructure and the ecological flows in the river. The identification of vulnerabilities makes it possible to determine whether it is appropriate to consider methods of adaptation to climate change for the municipalities under study.

The results of the study suggest that vulnerability is not evenly distributed across the greater Québec City metropolitan area. In fact, according to the available data, the municipalities of Côte-de-Beaupré are barely or not at all vulnerable to supply problems associated with severe low water levels in the watercourses, with very low probabilities of a shortage, today or in the future.

The vulnerabilities identified for the cities of Québec and Lévis are more significant. Despite the commissioning of high-capacity interconnections in Québec City, the risk of a shortage tends to increase over time in Québec City due to the worsening of summer low-water conditions and the increase in water needs.

For the city of Lévis, the results indicate a relatively limited risk of shortage associated with changes in the hydrology of the Chaudière River and water needs. However, the uncertainty surrounding the shift of the salt front and the lack of interconnection between the water supply systems, which would mitigate production deficits during summer consumption peaks, warrants the city continuing its efforts to reduce the vulnerability of its system regardless of changes in river water availability.

• Ville de Québec

• Ville de Lévis

• Municipalité de Boischatel

• Municipalité de Château-Richer

• Municipalité de Beaupré

• MRC de la Côte-de-Beaupré

• Direction de l’expertise hydrique, MDDLECC