ClimateChange Assessment Guide.pdf - University of Waterloo

Background11• An increase in lake-effect snow in the Great Lakesregion has been recorded since 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).• The number of strong cyclones increased across theGreat Lakes region over the period 1900 to 1990(Angel and Isard, 1998).With higher temperatures in the Great Lakes basin, andsubsequently less snowfall, reductions in the depth, areaand duration of snow cover and increases to the lengthof the frost-free period (Great Lakes Water Quality Board(GLWQB), 2003) have been reported.2.2.2 Ontario’s Future ClimateProjected changes in Ontario climate are basedupon GCM simulations. GCMs are discussed in moredetail in the next chapter along with GHG emissionscenarios. While some of the projected changes inclimate presented in this section are based on globalor national research or assessments, many of them arerelevant to Ontario particularly as they build awarenesswith resource managers of trends that may occuror of potential impacts to consider in planning andmanagement.The greatest warming is likely to occur in northernOntario during winter (Chiotti and Lavender, 2008).Changes in extreme warm temperatures are expectedto be greater than changes in the annual meantemperature (Kharin and Zwiers, 2005). The number ofdays exceeding 30°C is projected to more than doubleby the year 2050 in southern Ontario (Hengeveld andWhitewood, 2005) and the number of severe heat dayscould triple in some cities by 2080 (Cheng et al., 2005).Heat waves and drought may become more frequentand long lasting.Most climate models are projecting that annualprecipitation totals will likely increase across Ontario.However, summer and fall amounts may decrease upto 10% in southern portions of the Province. Winterprecipitation may increase as much as 10% in the southand 40% in the north (Chiotti and Lavender, 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 (Burnett et al., 2003; Kunkel et al., 2002).Changes in extreme daily precipitation are expectedto be greater than changes to the annual amounts(Kharin and Zwiers, 2005). High intensity rainfall eventsare likely to be more frequent and intense (Trenberth etal., 2003), as projected using two GCMs, HadCM2 andCCCma. In the HadCM2 model, the frequency of lightand moderate one-day rainfall events are projected todecrease slightly while the frequency of heavy eventswill increase 57% (or 6% per decade) by 2080 to 2100.The CCCma model projects increases of 0.1 to 9% inlight and moderate events and an increase of 23% (2.5%per decade) in heavy events for this period. The CCCmaalso projects a 15 mm or 30% increase in future extremedaily rain amounts by 2080 to 2100, or 3% increaseper decade, for the 20-year return period over 1975 to1995 amounts (Kharin and Zwiers, 2000). Observed andprojected changes for Canada that inform the Ontariocontext are summarized in Table 2.5.