Centered on historic baseline assessments, summer and early fall in southern Ontario are typically marked by decreased water availability during naturally occurring periods of increased evapotranspiration and its corresponding low precipitation (Sutherland, 2016; Morris et al., 2008). Lower precipitation subsequently results in a reduction in water levels that affect both surface and groundwater availability. Consequently, coupled with the already uncertain water supply during these seasons (i.e., reduced water levels in drier months), there is a corresponding increase in water demand among various domestic, industrial and agricultural water users, therefore posing a threat to equitable water allocation and distribution among users (Bonsal et al., 2011; Morris et al., 2008; Shortt et al., 2004).
In the Canadian context, the sub-watersheds in the Province of Ontario lose the highest amount of water naturally by evaporation during the summer months as compared to other Canadian provinces (Bonsal et al., 2011). Further exacerbating the vulnerability of Ontario’s water quantity in the summer months, various greenhouse gas scenarios are projecting that southern Ontario is particularly susceptible to an increase in both the frequency and intensity of droughts due to increasing mean temperatures (McDermid et al., 2015; Wang et al., 2014). With increasing surface temperatures, more volumes of water sources are lost due to evaporation; thus lowering lake and groundwater levels. Changes to the hydrologic cycle will likely include alterations in the timing, rate, and volume of water that recharges groundwater systems. This will subsequently have a ‘ripple effect’ on surface water resources, wherein the quality and availability of surface and groundwater for drinking supply and maintaining valued ecosystems (i.e., cold water fish in streams) will also likely be affected by changes in thermal temperature
(Grannemann & Van Stempvoort, 2016). With these hydrologic factors under consideration, changes to the rate of water replenishment (i.e., recharge-discharge) between surface and groundwater levels across the province are likely to affect humans and ecosystems.
The projections of future climate change for the Province of Ontario pose serious concerns regarding the quality and availability of future water resources. Warming is projected across the entire province throughout the 21st century, with the greatest increase (as anticipated by various climate scenarios) projected to be upwards of 10.3 degrees Celsius by 2080 (McDermid et al., 2015). Across the province, warming is projected to increase winter temperatures ranging from 1.1 to 3.9 degrees Celsius, and in the summer periods warming is projected to increase temperatures ranging from 1.2 to 9.8 degrees Celsius by 2080 (McDermid et al., 2015). Moreover, Wang et al. (2014) predict a likely raise in mean temperature in Ontario to 6 to 8 degrees Celsius by the end of the century (7). These projections are indicative of more frequent and intense droughts in the region that illustrate a threat to future water quality and availability.
The literature suggests that temperature is one of the most important drivers in maintaining healthy aquatic ecosystems (Maghrebi et al., 2015), and that species are physiologically adapted to specific thermal temperatures such that “the availability of suitable thermal habitat has an influence on their growth, survival, timing of reproductive events and distribution” (Grannemann & Van Stempvoort, 2016, 40). Accordingly, changes to water temperature from climate change will not only affect humans by a lesser supply of potable water, but it will also impact freshwater organisms that depend on specific thermal temperatures for their survival.
In addition to the projected mean temperature increases in southern Ontario, studies have quantified its corresponding impacts on changes in total precipitation. By 2080, more precipitation is projected in the winter (i.e., upwards of 158 mm from historic mean levels) and less precipitation is projected in the summer (i.e., with a range of 69 to 48 mm less precipitation than historic baseline levels across the province) (McDermid et al., 2015). The imbalance of precipitation levels indicates increased snowfall and flooding in the winter, and decreased rain in
the summer months; when water resources are already stressed by naturally occurring dry periods with low precipitation. Moreover, hotter mean temperatures is likely to increase water demand among domestic, industrial, agricultural, and various other sectors, in response to the increased temperatures and reduced water availability.
Changes in mean temperature and precipitation levels are not the only factors of climate change that are likely to impact source water quality and availability. Within the GTA, the Toronto and Region Conservation Authority (TRCA) discuss that changes in climate are also likely to affect water quality and quantity, in addition to wastewater infrastructure. Accordingly, the TRCA describe that at times of extreme precipitation events, heavy rain can force wastewater to enter rivers and streams, it can damage infrastructure, erode stream and river banks, and flush polluting substances (e.g., oil, lawn fertilizers and animal waste) into waterways (TRCA, 2019b, para. 9). In contrast, at times of little amounts of precipitation, the TRCA discuss that warmer water temperatures and increased evapotranspiration in the Great Lakes and other various interconnected water bodies may allow new waterborne pathogens to move northward or existing ones to flourish (TRCA, 2019b). The introduction of new waterborne pathogens is particularly worrisome, and Moreira & Bondelind (2016) emphasize that the occurrence of waterborne disease outbreak may have significant impacts for drinking water, and that due to climate change and its increased potential for waterborne disease outbreak, “drinking water treatment plants are likely to face increased uncertainty in safeguarding the quality of its water” (83).
In review of the overall projected climate change scenarios in Ontario, there appears to be an imbalance in the projected levels of precipitation, such that the winter seasons are projected to receive an excess amount of precipitation, whereas in the summer (drier) months there is an anticipated lesser amount of precipitation. In either case, the adverse effects of climate change on freshwater systems can aggravate the impacts of other human stressors, such as population growth, continuous and growing economic activity, urban expansion and its associated land use change, surface water contamination, and over-taking of groundwater.
Globally, water demand is likely to grow in the coming decades, primarily due to climate change, population growth and its corresponding increased demand for water to serve the
growing human needs for drinking, irrigation and the economy. Climate change impacts, such as higher mean terrestrial and aquatic temperatures, and increased precipitation variability, are predicted to impact southern Ontario. Given the past, current and future susceptibility of southern Ontario to experience water quality and quantity issues, water supply is likely to remain uncertain amidst climate change, population growth, and various other pressures.