ClimateChange Assessment Guide.pdf - University of Waterloo

Climate Change Assessment87Table 6.8 continuedClimate Parameter Statistic/Metric of Comparison CommentsAverage annual days with precipitation Relevant to Downscaled climates onlyMaximum hourly precipitationRelevant to Downscaled climates onlyAverage annual maximum drought Relevant to Downscaled climates onlySolar Radiation Monthly and Annual Totals Total energy flux is main interestWind Speed/Travel Monthly and Annual Averages Extremes are not of interestPotential Evapotranspiration Monthly and Annual Totals Extremes are not of interest6.6 Assessment of Hydrologic ImpactsThe potential hydrologic impacts of future climatechange will often be assessed by comparing theestimated streamflow for future climate scenarios againstcurrent hydrologic conditions. Streamflow varies in themagnitude, duration, and frequency of high and lowflow events. The statistical metrics are calculated fromsimulated results and analyzed to estimate changes fromcurrent conditions.Streamflow regimes are a function of climate, geology,vegetation, topography, land use, and hydraulicinfrastructure (e.g., dams). When any of these conditionschange, scientists and engineers are interested in theimpact of these changes on the regime. As such, avariety of statistical techniques to quantify those changeshave been developed. While historical investigationshave focussed on changes to peak streamflow, today’swater managers have broadened their assessments toevaluate the change over the whole streamflow regime.This can include consideration of seasonal variability oflow and high flows that influence many of the ecologicalflow requirements.When conducting an assessment of potential hydrologicimpacts from climate change, it is recommended thatwater resources practitioners follow the followingprocess:• Identify reference regime;• Select metrics and identify standards /targets;• Setup future conditions model(s);• Model climate change impacts by scenario;• Compare changes in climate data;• Compare hydrologic changes by scenario; and• Consider uncertainty.6.6.1 Identify Reference RegimeThe first step in completing a climate change hydrologicimpact assessment is the selection of the appropriatereference regime. The reference regime correspondsto the existing or baseline hydrologic conditions thatwill be compared against those simulated under futureclimate scenarios. The criteria for selection of baselineconditions are discussed in Section 6.4.1.When conducting the hydrologic impact assessmentusing computed monthly change fields, those changefields would be calculated with respect to observedclimate data for a range of years (e.g., 1961-1990). Inthis case, the reference hydrologic regime would be1961-1990 climate data and the time series of streamflowestimated during that same period of time.Guidance:In hydrologic climate change impactassessments, the reference regime and futureclimate scenarios should be simulated using thesame calibrated hydrologic model.Using the same model for both the reference regimeand future streamflow simulation enables the estimatedhydrologic changes to be attributed specifically tochanges in input climate data.6.6.2 Select Metrics and Identify StandardsScientists and engineers have developed a numberof statistical techniques to quantify changes in awatercourse’s flow regime. Table 6.9 summarizes some ofthese methods.