Expected consequences of worsening severe water shortages in Quebec (CASCADES project)

In recent years, Quebec experienced severe water deficits, particularly during the summers of 2020 and 2021. These events will worsen in duration, magnitude and severity over the coming decades due to climate change. Moreover, despite the growing importance of this issue, the consequences for ecosystems and human uses remain poorly documented and difficult to project in the coming decades in Quebec. 
The CASCADES project aims to develop the knowledge required for Quebec to prepare and adapt to the expected deterioration in the availability of water resources.

• Identify the main consequences of severe low water episodes on ecosystems, human uses, and the health and well-being of populations

• Identify the hydrological regions most likely to be affected in the future

• Identify gaps in our understanding of the issues and impacts associated with water availability during severe low water periods in order to orient future research

• Review of the literature on the consequences of severe low water levels and severe water scarcity episodes on ecosystems, human uses, and the health and well-being of populations

• Data collection to identify the worst water scarcity events that have occurred in Quebec under the integrated water management by watershed, and their observed consequences

• Development of narrative frameworks through hydrological and socio-economic scenarios

• Projection of the expected impacts on human uses

• Characterization of the expected impacts on human uses

Conducting a review of the water shortage episodes in recent years made it possible to describe the many issues and consequences in Quebec, particularly in the south of the province: difficulty in supplying surface water and groundwater for many municipalities and residents with private wells; increased water treatment costs, particularly due to the reduction of dilution factors;  prohibitions on using water outdoors; irrigation difficulties for agricultural producers; and various consequences for boating.  
For future water shortage episodes, with no adaptation or anticipation in the integrated management of water resources, all the consequences that were experienced during the previous events will be exacerbated in 2045 (+2°C scenario) and in 2065 (+3°C scenario). This will be particularly true in the St. Lawrence Lowlands, which will have a direct impact on the areas south of the St. Lawrence (Montérégie,  Estrie, Centre-du-Québec, Chaudière-Appalaches). See Figure 1.

Seven impacts on human uses have been identified as priorities:
•    Municipalities’ inability to meet the public’s high-priority and essential needs 
•    The inability to meet the public’s high-priority and essential needs through private wells and the additional costs engendered 
•    Halted residential development
•    Increased risks of boil water and drinking water avoidance advisories
•    Increased irrigation costs for agriculture
•    Reduced agricultural yields
•    Increasing tension between different water users in watersheds with reservoirs

The most worrisome consequences of severe low water levels for ecosystems are related to reduced water quality and changes in fish habitat, according to the literature review and consultations with experts. Changes in the physico-chemical parameters of the water (reduction in O2, variation in the natural pH of watercourses, increase in temperatures, etc.) and an increase in eutrophication phenomena are likely to profoundly alter the biological richness of watercourses and lead to significant imbalances in the populations of aquatic species.

Figure 1 : Number of projected consequences of severe water scarcity events under global warming scenarios of +2°C (2045) and +3°C (2065) relative to the pre-industrial period 1850-1950.

This project has made it possible to identify which knowledge should be prioritized for development. For example, for human uses: the impacts on industrial and commercial uses; the impacts on physical and mental health, the well-being of populations affected by episodes of severe water scarcity, including Indigenous populations, and on the social climate; the identification and analysis of conflicts over use; the operational vulnerability of drinking water production facilities in a future climate; the assessment of the water quality of private wells during periods of low water/drought; the implications for public health; and the prioritization of water uses in the context of drought.

• Jérémie Roques (ROBVQ)

• Bertrand Montel (AGÉCO)

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