ClimateChange Assessment Guide.pdf - University of Waterloo

E-12Guide for Assessment of Hydrological Effects of Climate Change in Ontario The hydrology of Subwatershed 19 is complex. In addition to natural hydrologic processes and sources of water inthe system there are several human influences with significant consequences. These include groundwater pumpingfor municipal potable water supply, wastewater discharges into the Credit River, storage in Island Lake with controlledoutflow and the many local incremental effects of agricultural development, aggregate extraction and urbanization.Tier Two Stress Assessment studies have determined that there is a risk of water supply shortages in the future,following further urban growth in the subwatershed (AquaResource, 2008).Because of the hydrologic complexity and the acute need for effective water management in the area, a linkedmodelling approach has been selected for the Subwatershed 19 Tier Three Local Area Risk Assessment study. Thisapproach has been selected for its inherent rigour and comprehensiveness. The approach will take advantage of thestrengths of two discrete models, a streamflow model and a groundwater model, to assess water resources. Thisapproach will also be employed in the climate change impact assessment.The streamflow generation model is used to generate continuous long-term time series of streamflow at sitesthroughout the subwatershed. The model partitions precipitation and snowmelt into runoff and groundwater recharge,while accounting for losses due to evapotranspiration (ET). Surface runoff and groundwater discharge are routedthrough the tributaries and Island Lake to the mouth of the subwatershed. The model is spatially and temporallydetailed so that it accounts for the varied landforms and physiography in the area and can capture the dynamicresponses in the system accompanying ever changing weather conditions and human activities. While streamflowmodels typically include a groundwater component to generate baseflow in streams, this component is typicallysimplistic and not capable of reflecting the temporal and spatial complexity of the groundwater system.The groundwater model, with a good three dimensional representation of the groundwater system (including pumpingwells), generates water levels and outflow to streams on a long-term steady state and transient basis. This modelrelies upon the spatially and temporally detailed recharge estimates provided by the streamflow model. In turn, thegroundwater model provides estimates of major groundwater transfers across subwatershed boundaries to thestreamflow model. Knowledge of these subsurface transfers is critical to configuring the streamflow model so that itcan account for all of the sources and sinks of water in the study area. This process needs to be iterative in thepreliminary stages of model calibration so that reasonable estimates of recharge and groundwater movement can betransferred between models.CVC has experience with both types of simulation models and the capacity to support the model development.Therefore this approach is realistic considering the available resources and technical capacity and providessufficiently detailed simulation results to adequately reflect the sophisticated nature of the study area. CVC conducted a formal model selection process for the Water Quality Strategy (WQS) (CVC, 2008). The modellingobjectives of the WQS were similar to the Subwatershed 19 study, at a different spatial scale. That selection processconsidered CVC needs into the future and sought to identify technologies that could become part of the core toolboxassociated with watershed assessment. The tool selected, the Hydrological Simulation Program – FORTRAN (HSP-F) (Bicknell et al., 2001), is relevant to the Subwatershed 19 study, has the capabilities to achieve the modellingobjectives and technical requirements and has been successfully applied across the whole Credit River Watershed forhydrologic and water quality assessments. Furthermore, particularly relevant to climate change impact assessments,