Today climate change and its associated impacts have become the center of attention for water resources’ planners and researchers all over the world. The lack of concrete understanding of the potential risks associated with these impacts and the fact that they will not be uniform across the world added to the complexity of the task. Currently, studies show that climate change will have an impact on reservoir water supplies in terms of both quality and quantity. Therefore, when designing for future water treatment processes, designers have to factor the climate change projections into their systems’ designs and operations. As a result, The Water Research Foundation in its report Assessment of the Impacts of Climate Change on Reservoir Water Quality examined how climate change alters the risks facing the reservoirs’ water quality. The aim of this research was to enhance the estimation of the future potential impacts of climate change on water reservoirs, quantitively, through designing and testing a new approach.
According to the Intergovernmental Panel on Climate Change (IPCC), due to climate change, freshwater resources are expected to be scarce all over the world, especially in arid and semi-arid areas. Moreover, climate change poses a risk to the quality of potable water as it will accelerate the growth of algae and increase the frequency of cyanobacterial blooms in the reservoirs which will affect the safe water supply to humans. Hence, the researchers focused their efforts on trying to find ways to reduce these potential impacts and provide tools to prevent them.
The researchers identified the increase in algal growth, turbidity, and dissolved organic carbon (DOC) loads as the most-likely impacts of the climate change on the reservoirs. Therefore, the research team used an integrated modeling scheme to study three potable water supply reservoirs. The choice of these reservoirs took into account the type of climate in which the reservoirs are located, their role in the potable water supply chain, and the availability of historical data as the research team believed that this would be the best way to measure the potential impacts of climate change and compare the resilience of the different water supply systems; these chosen reservoirs were: Hsin-Shan Reservoir in Taiwan; Occoquan Reservoir in Virginia, USA; and Myponga Reservoir in Australia.
Regarding the Hsin-Shan Reservoir, this reservoir is located in Northern Taiwan and is the largest drinking water source in the region. The reservoir is found in a humid, sub-tropical climate, and located in a tropical cyclone area. For this reservoir, the researchers examined the negative impacts of climate change on the water quality, both, in the near term (2020–2039) and long-term (2080–2099). This reservoir is both small and deep in size which increases the vulnerability of the quality of its water to climate change, especially from thermal stratification. From the collected data, the research team deduced that there is an increase in the intensity of the tropical cyclone activity due to the rise in atmospheric water vapor and surface water temperature from a warming climate. Moreover, they concluded that an increase in atmospheric temperature was the primary reason for the lower water quality in the reservoir because it will lower the dissolved oxygen concentrations and release more phosphorus from the sediments.
On the other hand, the Occoquan Reservoir is located in Northern Virginia in which The Upper Broad Run and Middle Broad Run watersheds can be found in its northwestern part. These watersheds drain into Lake Manassas which is an artificial lake that is a vital potable water supply for the surrounding area. The climate in the reservoir’s area is classified as temperate, and the area experiences four distinct seasons. The research team projected the potential impacts using two models based on the mean yearly precipitations and the mean yearly surface air temperature. These parameters were chosen to depict the upper and lower limits of the other different models and to denote a “hot and wet” and “cool and dry” climate conditions. From these models, the researchers were able to conclude that there will be a future thermal stratification in Lake Manassas which can expand and intensify thanks to the global climate change. Furthermore, increased water flow in the streams and channels is expected due to climate change which will result in an increase in nutrients pollution in the reservoir. Nevertheless, Lake Manassas could serve as a mitigator of these negative impacts within the reservoir and increase the resiliency of the region to the adverse effects of climate change.
Finally, regarding The Myponga Reservoir, this reservoir is located in Southern Adelaide and receives water from a natural catchment. This region has a Mediterranean-like climate with hot, dry summers and mild winters and the water is treated through a conventional treatment process that comprises of flocculation and chlorination at a close by water treatment plant. The results of the experiments done on this reservoir show that the water quality of the reservoir will suffer significantly from the higher demand. Moreover, from the modeling simulations and the data collected, the research team is confident that the Myponga River will most probably stop supplying water to the Myponga Reservoir in the future because the rising temperatures may result in less precipitation. In addition, they believe that a decreased inflow from the catchment and increased evaporation will put future stress on this particular water system; and that the nutrient loading will decrease due to the drop in both concentration and volume. Nonetheless, this recent decrease might not lead to less productivity from the reservoir because the internal nutrient cycle will be able to maintain this productivity.
From all the above observations, the researchers believe that it is vital to actively manage the watersheds to stop and control the contaminant runoff. To achieve this objective, the use of an integrated-modeling approach can help inform business-related future risks related to catchment-derived nutrients, DOC, and microbial contamination. In conclusion, based on the research findings, a number of conclusions can be reached: first, where air temperatures increase, surface water temperatures will rise. Second, the increase in temperature will impact the nutrient dynamics based on stratification behavior and intensify the phytoplankton productivity. Finally, the researchers recommend that destratification approaches to be implemented in the future designs and operations of the water reservoirs, as well as, the solutions to prevent and control contaminant runoff. Ultimately, utilities will have to develop more proactive strategies to lower the amount of in-stream and nonpoint source nutrient loads.