ClimateChange Assessment Guide.pdf - University of Waterloo

Guide for Assessment of Hydrologic Effects of Climate Change in Ontariovi• Increased night-time temperatures in the summer hasbeen linked to more intense convective activity andrainfall contributing to greater annual precipitationtotals (Dessens, 1995).• The number of strong cyclones increased significantlyacross the Great Lakes over the period 1900 to 1990(Angel and Isard, 1998).• Heavier, more frequent and intense rainfall eventshave been detected in the Great Lakes Basin sincethe 1970s.• The maximum intensity for one-day, 60-minuteand 30-minute duration rainfall events increasedon average by 3-5% per decade from 1970 to 1998(Adamowski et al., 2003).• The frequency of intense daily rain events increasedfrom 0.9% (1910 to 1970) to 7.2% (1970 to 1999) forvery heavy events and from 1.5% to 14.1% for extremeevents (Soil and Water Conservation Society, 2003) forthe same periods.• An increase in lake-effect snow has been recordedsince 1915 (Burnett et al., 2003).• Precipitation as snow in the spring and fall hasdecreased significantly in the Great Lakes-St.Lawrence basin between 1895 and 1995, althoughtotal annual precipitation has increased, (Mekis andHogg, 1999).Projected Changes in Ontario’s ClimateProjected changes in Ontario climate are based uponGCM simulations. Over 30 different GCM-scenariocombinations indicate that total annual precipitationcould increase by 2 to 6%, while temperatures couldincrease by 2 to 4ºC by the 2050s over the Great LakesBasin (Bruce et al., 2003). The greatest warming is likelyto occur in Northern Ontario during winter. Changes inextreme warm temperatures are expected to be greaterthan changes in the annual mean temperature (Kharinand Zwiers, 2005). The number of days exceeding 30°C isprojected to more than double by the 2050s in SouthernOntario (Hengeveld and Whitewood, 2005) and thenumber of severe heat days could triple in some cities bythe 2080s (Cheng et al., 2005). Heat waves and droughtmay become more frequent and long lasting.Most climate modelling results suggest that annualprecipitation totals will likely increase across Ontario;however, summer and fall precipitation amounts maydecrease up to 10% in southern portions of the Province.Winter precipitation may increase as much as 10% in thesouth and 40% in the north (Lemmen et al., 2008). Morewinter precipitation is very likely to fall as rain. Lakeeffectsnow will likely increase until the end of the 21stcentury, then snowfall may be replaced by lake-effectrainfall events (Kunkel et al., 2002; Burnett et al., 2003).Extreme rainfall events in Ontario are expected toincrease by 5% per decade while severe winter stormsincrease in intensity. Thirty minute and daily extremerainfall may increase by 5% and 3% per decade,respectively (Bruce et al., 2006b).Hydrologic Studies and Climate ChangeManagers can explore a range of adaptation strategiesthat expand the coping range of a hydrologic systemby considering the potential impacts of climate change.Since we can no longer rely on historical trends toguide our planning for the future, water resourcemanagers must look forward by examining the possibleconsequences of a wide range of plausible futureclimates. Climate change impact assessment providesinsight into future directions in terms of water resourcesystem response and behaviour.Climate change has the potential to affect both theavailability of water for municipal uses and the qualityof that water. The Clean Water Act of 2006 and theDrinking Water Source Protection program instituteda series of technical studies across the Province; theresults of these studies may be significantly altered bychanging climates. For example, more intense rainfallreduces recharge rates, more prolonged droughtincreases the need for stored water supplies, and higherevapotranspiration can reduce the amount of water inreservoirs. Water quality may be degraded by increasedaquatic plant growth instream as a result of climatechange. Also, more intense rainfall may result in greaterrates of soil and streambank erosion and transport of soilbound pollutants to streams.The Permit-to-Take-Water (PTTW) program will beaffected by changing climates. With warmer instreamwater temperatures and higher evapotranspiration,streamflow may be reduced to levels that threatenaquatic communities and water supplies. Seasonalredistribution of precipitation may result in lowerstreamflow on a seasonal basis. Water users may findtheir needs changing in the future as climates change.For example, agricultural irrigation and golf course