ClimateChange Assessment Guide.pdf - University of Waterloo

E-48Guide for Assessment of Hydrological Effects of Climate Change in Ontario The Clean Water Act (2006) was introduced by the Province of Ontario to ensure communities are capable ofprotecting their municipal water supplies through the development of collaborative, locally driven, science-basedsource water protection plans. Communities will identify potential risks to local water supply sources and will takeaction to reduce or eliminate these risks. The Act was designed to identify threats to both water quality and waterquantity. The Ministry of Environment’s Technical Rules (2009), Part III describes the specific technical requirementsof the three water budget tiers which are completed to identify threats to water quantity, as follows:• Tier One Water Budget and Subwatershed Stress Assessment. The goal of the Tier One Water Budgetand Water Quantity Stress Assessment is to estimate cumulative hydrologic stresses placed on asubwatershed. The study team undertaking the Tier One Assessment will estimate the percent waterdemand, the percentage of water supply that is demanded by water users. Watersheds where the percentwater demand is determined to be above a benchmark threshold value are termed ‘moderately’ or‘significantly stressed’. Watersheds calculated as having a low percent water demand are termed ‘low stresswatersheds’ and will not be subject to additional water budget requirements.• Tier Two Water Budget and Subwatershed Stress Assessment. Tier Two Subwatershed StressAssessments are completed to verify the results of the Tier One Stress Assessment using additional data andnumerical water budgeting tools. The Tier Two Water Budgets are developed at the subwatershed scale,similar to the Tier One level, and they require a continuous surface water model and a calibrated groundwaterflow model.• Tier Three Water Budget and Local Area Risk Assessment. The objective of the Tier Three WaterQuantity Risk Assessment is to estimate the likelihood that municipalities will be able meet future waterquantity requirements. A Tier Three Risk Assessment is carried out on all municipal water supplies located insubwatersheds that were classified in the Tier Two Assessment as having a ‘moderate’ or ‘significant’potential for hydrologic stress. The Tier Three Assessment uses refined surface and/or groundwater flowmodels, and involves a much more detailed study of the groundwater or surface water sources available.CVC has completed a Tier Two Water Budget and Subwatershed Stress Assessment following the Technical Rulesand published the results in the Tier Two Integrated Water Budget Report (CVC, 2009). This report outlines thetechnical work required to complete the Tier Two Stress Assessment, including; development of consumptive waterdemand estimates, the development and calibration of groundwater and surface water models, and the completion ofthe subwatershed stress assessment.As a result of the Tier Two Stress Assessment, CVC was required to complete Tier Three Risk Assessments forSubwatersheds 10, 11, and 19, all of which contain municipal groundwater supplies. In 2006, The Ministry of NaturalResources (MNR) initiated a Tier Three Pilot Project for Subwatershed 19 containing the municipalities of Orangeville,Mono, and Amaranth. The purpose of this pilot study was to test and demonstrate the methodologies needed tocomplete the Tier Three Risk Assessment and to modify those methodologies where required based on the results ofthe pilot study.This case study demonstrates how the climate change impact assessment may be incorporated into a Tier Two orTier Three assessment based on CVC’s Tier Two and Tier Three experiences. The case study documented hereinshould be considered as an example, as the climate change impact assessment was completed specifically to supportthis case study and may not be consistent with future work completed by the Source Protection Authority.