ClimateChange Assessment Guide.pdf - University of Waterloo

Climate Change Assessment59Further, no hydrologic model is completely deterministicand the assumptions and parameterization used toapproximate processes, which cannot be fully describedphysically and mathematically, differ between modellingalgorithms and codes. As such, there is the potential fordifferent modelling software to produce different resultsregardless of the quality of model set-up and calibration.This should also be taken into account in the analysis ofresults.Guidance:Confidence in simulation results must beaddressed so that model results can be properlyinterpreted.Ignoring this step of the assessment may lead toimproper conclusions drawn from results, as the causeand effect relationships may be misinterpreted.Simulation confidence may be estimated by identifyingall possible sources of error, their relative magnitude andthe manner in which these compound to affect results.Some form of error analysis may be conducted, suchas a Monte Carlo analysis, wherein many model runsare made with selected parameters varying within theirenvelope of uncertainty. This creates an overall envelopeof outcomes that can be used to estimate confidenceintervals. This level of analysis is very demanding ofresources. Confidence can be expressed in terms ofmodel accuracy in simulating short or long-term flowvolumes, extreme events or flow frequency distributions.Differences in simulation results between scenariosthat are within the range of the confidence intervalare considered not significant. In this context, notsignificant implies that trends may exist but differencesare too small to confirm these trends conclusively.6.3.4 SummaryAfter completing the tasks in this section the modellershould have:• Acquired all necessary data for model setup andtesting;• Setup the model for current conditions;• Calibrated and validated the model for all seasonsand weather conditions; and• Estimated error and confidence intervals associatedwith model simulation results6.4 Select Climate ScenariosWith the wide array of emission scenarios and GCMsavailable, one of the significant challenges in climatechange impact assessment is the selection of climatescenarios. This section addresses the issues involvedin scenario selection and provides a rationale foridentifying a group of scenarios for the assessment.A number of overarching, generic criteria havebeen articulated by the IPCC scenario-developmentcommunity to assist in providing guidance ondetermining both the acceptability of climate changescenarios for hydrologic assessments and the usefulnessto policy makers and decision makers irrespective of thescenario-generating technique (IPCC-TGICA et al., 2007;Smith and Hulme, 1998). They include:• Criterion 1: Consistent with global projections.Climate scenarios used should be consistent with abroad range of global warming projections based onincreasing concentrations of greenhouse gases. Usingthe most recent findings reported in the IPCC AR4,the range in global temperature increase is 1.1°C to6.4°C (likely range) and 1.8 °C to 4.0°C (best estimate)by 2100 (Intergovernmental Panel on Climate Change(IPCC), 2007c).• Criterion 2: Physically plausible. The climatescenarios should be physically plausible; they mustuphold the basic laws of physics. If a suite of climatevariables are used in climate scenario development,the combination of changes in these variables (whichare often correlated) should be physically consistentand reasonable. Similarly, changes in one regionshould be physically consistent with patterns both inanother region and globally.• Criterion 3: Applicable in impact assessments. Theclimate scenarios should describe projected changesin the range of variables that are pertinent to thehydrologic assessment. The variables should beprovided at the most relevant spatial and temporalscale for the hydrologic assessment.• Criterion 4: Representative. The selected climatechange scenarios should encompass a wide aspossible range of future regional climate changes.