ClimateChange Assessment Guide.pdf - University of Waterloo

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Guide for Assessment of Hydrologic Effects of Climate Change in Ontarioivsubwatershed studies, environmental monitoring, anddam and reservoir management; discusses future climatescenarios along with GCMs and greenhouse gas (GHG)emission scenarios; identifies methods for developingfuture local climates; examines the hydrologic impactsof climate change with respect to critical hydrologicprocesses, with past studies conducted in Ontariopresented; and presents a step-by-step methodology forplanning and conducting hydrologic and climate changeimpact assessments in the final chapter.A case study, included in Appendix E, tests anddemonstrates a climate change impact assessmentconducted following the recommended methods. Thesubject area for the case study is Subwatershed 19 inthe Credit River Watershed. This area, surrounding theTown of Orangeville, is the subject of a Tier Three WaterBudget and Local Area Risk Assessment for the purposeof Source Water Protection.Observed Global Climate ChangeThe Fourth Assessment Report (AR4) of theIntergovernmental Panel on Climate Change (IPCC)stated that “[w]arming of the climate system isunequivocal, as is now evident from observations ofincreases in global average air and ocean temperatures,widespread melting of snow and ice and rising globalaverage sea level” (Intergovernmental Panel on ClimateChange (IPCC), 2007b 30). In addition to global changes,long-term continental, regional and ocean-scale changesin climate have also been observed and are reflected inchanges to arctic temperatures, ice, extremes (droughts,heavy precipitation and heat waves), and wind patterns.Moreover, the human influence extends beyond globaltemperature to other aspects of climate, includingocean warming, continental-average temperatures,temperature extremes and wind patterns.Observed global changes in climate relevant to waterresources are summarized in the following table.Observed changes in global climate relevant towater resources (Intergovernmental Panel on ClimateChange (IPCC), 2001b; Solomon et al., 2007; Bates etal., 2008)Observed Changes• Increase in the number, frequency and intensity ofheavy precipitation events, even in areas where totalprecipitation has decreased.• Decrease in snow cover in most areas of thecryosphere, especially during the spring and summermonths• Higher water temperatures in lakes.• Reductions (approximately two weeks) in the annualduration of lake and river ice cover in the mid andhigh latitudes of the Northern Hemisphere.• Increase in actual evapotranspiration from 1950to 2000 over most dry regions of the USA andRussia (greater availability of water on or near landsurface from increased precipitation and largeratmospheric capacity for water vapour due to highertemperature).• Increase in annual runoff in high latitudes andsome regions of the USA (decrease in West Africa,southern Europe and southernmost South America).• Altered river flow in regions where winterprecipitation falls as snow; more winter precipitationfalling as rain.• Earlier snowmelt, due to warmer temperatures.• Fewer numbers of frost days, cold days, cold nightsand more frequent hot days and hot nights.• Decrease in diurnal temperature range (0.07°C perdecade) between 1950 and 2004 but little changefrom 1979 to 2004 as maximum and minimumtemperatures increase at the same rate.Projected Global Climate ChangeModelling experiments exploring the sensitivity of theclimate system to rising concentrations of greenhousegases (GHGs) project an increase in the globalmean surface air temperature over the 21st century(Intergovernmental Panel on Climate Change (IPCC),
Executive Summaryv2007c). The magnitude of the warming is related tothe emission of GHGs and resultant concentrationsof those gases in the atmosphere and their radiativeforcing. The best estimate for the global averagetemperature increase for 2090-2099 relative to 1980-1999is 1.8°C to 4.0°C if all emission scenarios are considered(Intergovernmental Panel on Climate Change (IPCC),2007c).Warming is projected to be greatest over land and mosthigh northern latitudes and the least in the SouthernOcean and parts of North Atlantic Ocean. In mostareas of North America, the increase in annual meantemperature is greater than the global mean citedabove. The most warming is likely to occur in winter innorthern regions and in summer in the south westernUSA. Minimum winter temperatures are likely to increasemore than average temperatures in northern NorthAmerica.Warming generally increases the spatial variability ofprecipitation. Rainfall in the subtropics is projected todecrease and precipitation is projected to increase athigher latitudes (Christensen et al., 2007b). In Canadaand northeast USA, annual precipitation is very likelyto increase and it is likely to decrease in the southwestUSA. The seasonal distribution of precipitation is alsoaffected; winter and spring precipitation in southernCanada is likely to increase and summer precipitationis likely to decrease. The snow season length and snowdepth are expected to decrease except in northernmostCanada where the maximum snow depth will likelyincrease (Christensen et al., 2007b). The following tablelists some projected changes in global climate relevantto water.Projected changes in global climate as they relate towater (Meehl et al., 2007; Bates et al., 2008)Observed Changes• Hot extremes and heat waves will very likely be moreintense, frequent and longer in duration.• Number of frost days in middle and high latitudesdecrease and growing season lengthens.• Increased likelihood of summer drying in midlatitudesand associated risk of drought (increasingfrom 1% of present-day land area to 30% by 2100).Observed Changes• Increase in number of consecutive dry days.• Very likely that heavy precipitation events willbecome more frequent.• Increase in the amount and intensity of precipitationat high latitudes and in tropics; decreases in somesub-tropical and lower mid-latitude regions.• Area of snow cover projected to contract, glaciers/ice caps lose mass; in many areas summer melting isgreater than winter snowfall accumulation.• By 2050, permafrost area in Northern Hemispherelikely to decrease 20-35%; increases in thaw depth.• Potential evaporation projected to increase(atmosphere’s water-holding capacity increases withhigher temperatures but relative humidity stayssame); increase in water vapour deficit.• Runoff increases in high latitudes and wet tropics,decreases in mid-latitudes and some parts of drytropics.Observed Changes in Ontario’s ClimateChanges in the climate system have also been observedat the local scale – in Ontario and within the Great LakesBasin, as summarized below:• Annual average air temperatures across the provinceincreased from 0 to 1.4°C; the greatest warmingoccurred in the spring for the period 1948 to 2006,(Lemmen et al., 2008).• The number of warm days and night-time wintertemperatures increased between 1951 and 2003(Bruce et al., 2006a).• Total annual precipitation increased 5-35% since1900, (Zhang et al., 2000) and the number of days withprecipitation (rain and snow) increased (Vincent andMekis, 2006).• Water vapour in the Great Lakes Basin and SouthernOntario has increased more than 3% from 1973 to1995, contributing to higher intensity rainfall events(Ross and Elliott, 2001).
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Hydrological Impacts39frequency of
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Climate Change Assessment6. Climate
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Appendix A A-1Watershed and Receivi
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Appendix A A-3Watershed and Receivi
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Appendix B B-1GCM Modelling GroupsT
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Appendix CGCM-Based Change FieldAss
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C-2Guide for Assessment of Hydrolog
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C-10Guide for Assessment of Hydrolo
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Appendix DRCM and GCM Data Conversi
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Appendix E E-1Subwatershed 19 Case
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