ClimateChange Assessment Guide.pdf - University of Waterloo

Background9Table 2.3 Projected changes in global climate as they relate to water (Bates et al., 2008; Meehl et al., 2007)Projected Changes• Hot extremes and heat waves will very likely be more intense, frequent and longer in duration.• Number of frost days in middle and high latitudes decrease and growing season lengthens.• Increased likelihood of summer drying in mid-latitudes and associated risk of drought (increasing from 1% ofpresent-day land area to 30% by 2100).• Increase in number of consecutive dry days.• Very likely that heavy precipitation events will become more frequent.• Increase in the amount and intensity of precipitation at high latitudes and in tropics; decreases in some subtropicaland lower mid-latitude regions.• Area of snow cover projected to contract, glaciers/ice caps lose mass; in many areas summer melting is greaterthan winter snowfall accumulation.• By 2050, permafrost area in Northern Hemisphere likely to decrease 20-35%; increases in thaw depth.• Potential evaporation projected to increase (atmosphere’s water-holding capacity increases with highertemperatures but relative humidity stays same); increase in water vapour deficit.• Runoff increases in high latitudes and wet tropics, decreases in mid-latitudes and some parts of dry tropics.Impacts of climate change occur due to changes inmean conditions and changes in variability includingthe sequence, frequency, duration and intensity ofextreme events. Extreme events, rather than changes inmean conditions, are often more relevant to assessingthe impacts of a changing climate. This is becausebiophysical and human systems are more likely tosuffer harm from these extreme events which are oftenoutside coping capacity, than from changes in themean conditions. Some projected changes in extremeevents, and their likelihood of occurring, are summarizedin Table 2.4. Note that the IPCC has developedterminology to clarify uncertainty by relating confidencein being correct to the likelihood of an occurrence oroutcome; these findings use that language.A changing climate is likely to affect global wateravailability; many regions that are already hydrologicallychallengedwill experience further stress with climatechange. But how will Ontario fare in the future?