ClimateChange Assessment Guide.pdf - University of Waterloo

Hydrological Impacts45reduce the storm peak flow rates thus, attenuating thehydrograph. Attenuation results in reduced storm peakflow as well as a lengthening of the time for the stormto pass through the system. Climate change may havesome limited impact on routing, by altering the hydraulicconditions in the stream channel. Floodplain vegetationgrowth could change channel conveyance characteristicsand affect change in the channel geometry. Also, climatechange could reduce or eliminate ice formation instreamthat normally restricts flow during critical runoff periods.Annual streamflow is highly correlated to annualprecipitation, and is therefore expected to experiencesignificant increases under a changed climate. Theimpacts of climate change on the seasonal fluctuationsin streamflow are less well known, with such changescaused by shifts in the constituent hydrologicalprocesses that contribute to streamflow. Potentialimpacts to streamflows may include the following:• Increasing temperatures may shift the springsnowmelt to earlier in the year, implying that thespring freshet will follow the same shift. Similarly,baseflow recession will follow the same shift leadingto low flow periods occurring earlier in the year.• Increased temperatures may also result in a decreasein snow accumulation over the winter season, therebyreducing the magnitude of the spring freshet. Thefrequency of smaller, mid-winter melts would increase,causing winter flows to increase. The prevalence ofunfrozen soil conditions during these mid-wintermelts may significantly increase groundwater rechargeduring this time, and subsequently groundwaterdischarge.• It has been suggested that the frequency andintensity of storm events may increase as a result ofclimate change. Increased rainfall intensity promotessurface runoff over infiltration, thus increasingstreamflow in general and event based peak flows.• An increase in evapotranspiration may cause adecrease in the amount of recharge reaching thegroundwater. This recharge reduction may lead toa declining water table which is manifested as adecrease in baseflow to streams.5.2.5 Water QualityWhile this document is specifically relevant tohydrological studies, many programs also need tounderstand how climate change may affect waterquality in local streams and lakes. Most comprehensivehydrologic models also include some water qualitycomponents. Thus, water quality effects can besimulated and assessments conducted at this level. Inmany other studies sophisticated dynamic water qualitymodelling is not practical and a less rigorous qualitativeapproach may be required. As a guide to water qualityassessment, Table 5.1 provides a summary of the moresignificant and widespread consequences of climatechange in terms of processes affected and the resultanttrend in water quality by parameter.Table 5.1 Water Quality Effects of Climate Change.Process Directly Affected byClimate ChangeErosion and WashoffWater Quality ParametersAffectedSuspended Solids,Phosphorus, Heavy Metals,E.ColiDirect Effect on ParameterSecondary Effects/ConsequencesAquatic plant communitiescould be stimulated byincreased phosphorus levelsinstreamSame as aboveLess winter snowpack andmore rain on frozen groundwill increase overland erosionand pollutants in runoffMore severe storms mayresult in more significantoverland and instream erosionevents with higher instreampollutant loadingsMore precipitation overallcould raise erosion rates andpollutant levels in streamsSame as aboveTable 5.1 continued on next page