ClimateChange Assessment Guide.pdf - University of Waterloo

Guide for Assessment of Hydrologic Effects of Climate Change in Ontario14Meteorological data are fundamental inputs forhydrologic design applications or hydrologicassessments and investigations. A critical issue is that“due to a changing climate, the past climate andhydrologic experience may no longer be a reliableguide for decision making” [Baer, 2008, water]. A keyassumption in hydrologic planning and design, thestationarity of climate (i.e., the consistency of climatestatistics over time), is being challenged (Milly et al.,2008). Conventionally, water resource investigations haverelied on historical meteorological data to estimate therisk or likelihood of the occurrence of extreme stormsor periods of extreme low flow, or to define the waterbalance of a watershed, for example. Climate changeimpact assessments of hydrologic systems shouldexamine a wide range of plausible futures, scenarios,and levels of risk to build resilience into the systems.Consideration of multiple climate change scenarios, andtheir variable potential to result in widespread impacts,is needed to ensure the designed systems, policies andmanagement practices provide an acceptable level ofprotection in the future. The following sections outlinepossible implications of climate change for a variety ofwater resources programs and issues within the Provinceof Ontario.2.3.1 Drinking Water Source ProtectionFollowing recommendations made as part of theWalkerton Inquiry, the Province of Ontario passed theClean Water Act in 2006. The Clean Water Act ensuresthat communities identify both water quality and waterquantity risks related to their drinking water supplies,and if necessary, take actions to reduce these risks.Multi-stakeholder committees, including municipalities;conservation authorities; industrial, commercial andagricultural representatives; and community groups areactively engaged in completing technical studies tobetter characterize municipal water supplies and identifypossible threats and risks to those water supplies.Thus far, technical studies to identify water quality andquantity related threats have been limited to analyzinghistorical meteorological conditions. To consider climatevariability, drought scenarios have been investigatedas part of the water quantity risk assessment; however,no climate change impact assessments have beenundertaken. Future scenarios are included as part ofthe water quantity stress assessments, but are limitedto the 25-year projected water demand and land usechange and do not extend to consider changes inclimate. The future scenarios could be expanded toinclude climate change and this process change couldbe accommodated in the existing Water Quantity RiskAssessment Framework. This would give water resourcemanagers a wider range of the future water balance in awatershed.In addition to affecting water quantity, climate changehas the potential to adversely impact water qualityand may create additional water quality risks. Warmerwater temperatures promote vigorous aquatic plant/algal growth; which in turn causes extreme fluctuationsin dissolved oxygen, critical to the health of the localfishery. More intense rainfall events cause additionalsoil erosion, increasing nutrient loads and bacteriallevels within receiving waters. Extended droughts in thefuture could result in very low baseflow in streams andan increase in the extent of the headwater ephemeralstream system such that a loss of habitat would beexperienced.With the ability to characterize the future state of thewatershed and identify future threats, water resourcemanagers would be able to build adaptive measuresinto municipal water supply systems, and thereby reducethe risk of a significant shortages being experienced inthe future.2.3.2 Water Demand Estimates and Water AllocationPlanningWithin the Province of Ontario, the Ministry ofEnvironment (MOE) is responsible for regulating watertaking. The MOE requires most water users takinggreater than 50,000 L/d to apply for, and obtain a PermitTo Take Water (PTTW). The MOE reviews the PTTWapplications to ensure that the proposed taking doesnot interfere with surrounding water takings, or cause anadverse environmental impact.Future climates in Ontario are expected to bewarmer, affecting evapotranspiration, with more dryperiods and a seasonal redistribution in precipitation.This will lead to changes in runoff timing and wateravailability. When considering the impact of a changedclimate on water taking, the water availability and thepossible changes in water use requirements should beconsidered. For example, to offset possible increases