Projecting the Impact of Climate Change

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This article was published in the July/August 2011 issue of Water Canada. www.WaterCanada.net

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Projecting the Impact of Climate Change

  1. 1. ClimaTe Change The headwaters of the Credit River near Orangeville, Ontario. How-To Strategies Projecting the impact of climate change. By BOB WAlkeR ANd dAvid vAN vlieTCanada’s water resourCes Michael Garraway is the water budget over several decades, the interactions ofsCientists and enGineers generally coordinator with the Ontario Ministry processes that determine weather andagree that climate change will have of Natural Resources. According to climate. Numerous modelling centresan impact on our water; however, we Garraway, the Province recognizes that a around the world have developed GCMshave not incorporated climate change thorough understanding of the potential that are used for long-term (250-year)assessments into many of our water impacts of climate change on hydrology simulations to characterize the evolutionmanagement efforts. Will the water levels is important to develop climate change of temperature, precipitation, solarin the Great lakes decline? Will the rivers adaptation strategies. “To our knowledge, radiation, winds, and other parametersof the Prairies overflow their banks more the Guide is the first of its kind developed well into the future.often and will they sustain our needs in and is equally relevant for all Canadian GCMs produce global scale output atthe summer? How long will the glaciers water resource managers, planners and relatively coarse grid point spacings ofof the Rockies continue to support icy practitioners,” he says.rivers? While the state of climate change As described in the Water resource managers are recognizingscience and modelling technology Guide, water resourcehas not advanced sufficiently to make practitioners have two the need to develop adaptation andsingular and reliable predictions, it is broad considerations mitigation strategies to guard againstpractical and prudent for our industry when setting out toto use available resources and tools to project climate change anticipated changes at the local scale.evaluate the expected range of climate impacts: they need tochange impacts. develop or obtain future climate datasets, 250 to 400 kilometres. Simulations are Water resource managers are and they need to select a modelling or designed to characterize future climaterecognizing the need to develop assessment approach that suitably on an annual, seasonal, and monthlyadaptation and mitigation strategies to represents the hydrologic processes that basis. At present, there are more thanguard against anticipated changes at may be influenced by a changing climate. 60 future climate simulations availablethe local scale. To that end, the Ontario from the collaborative research of theMinistry of Natural Resources and Global climate models members of the intergovernmental PanelMinistry of the environment sponsored The primary tool used to estimate on Climate Change (iPCC).the development of the Guide for future climate are global climate models This large set of simulations is theAssessment of Hydrologic effects of (GCMs). GCMs are complex physically result of applying more than 20 GCMsClimate Change in Ontario, produced based three-dimensional models that to four greenhouse gas (GHG) emissionby eBNFlO and AquaResource inc. in represent the earth’s atmosphere, scenarios. The four emission scenarios2010. oceans, and land surfaces and simulate, have been developed by the iPCC and18 WATER CANADA july/AuGuST 2011 WAT e R C A N A d A . N e T
  2. 2. ClimaTe Changereflect atmospheric levels of GHGsunder four storylines, each representing Figure 1: Mean annual precipitation anda different future trend in terms of global temperature changes for 57 climate scenarioseconomy, demographics, governance, at a southern ontario location.technology, and GHG emission levels.While the iPCC considers each of theseoutcomes equally plausible, the climateoutcomes differ significantly in termsof annual and monthly temperatureand precipitation change from existingconditions at all model grid points. Thisdisparity is illustrated in Figure 1 and isdue to differences in the GCMs and theemission scenarios.downscaling simulationsWhen projecting possible hydrologicimpacts from climate change, waterresource practitioners are faced withthe challenge of developing or obtainingclimate datasets that reflect the temporaland spatial level of detail needed at thelocal scale. GCMs lack the local scaleparameterization and feedback fromlocally significant features (i.e., topographyWAT e R C A N A d A . N e T WATER CANADA july/AuGuST 2011 19
  3. 3. ClimaTe ChangeFigure 2: study area location. at a climate station in southern Ontario. This figure displays the significant level of disparity among GCM models and emission scenarios as mean annual temperatures range from +1.7 Celsius to +4.9 Celsius , while annual precipitation changes range from -6 per cent to +17 per cent. The percentile method selects 10 scenarios from this set. Five scenarios are selected based upon the simulated changes in temperature and five are selected based upon changes in precipitation. For both parameters, scenarios are selected that best represent the 5th, 25th, 50th, 75th and 95th percentiles. This subset represents the groups mean, variability and extremes. an ontario case study The Guide provides a case study demonstrating the application of the percentile method and change field approach to project the impact of climate change on the headwaters of the Credit River (Figure 2), near the Town of Orangeville, Ontario. The case study includes the application of a continuous streamflow generation model (HSP-F) and groundwater flow model (MOdFlOW) toand surface water) to reflect local scale of local observations, the local climate. estimate the hydrologic effects of a seriesclimate directly in model output. The change field method is a simple of future climate scenarios. Research institutions continue to approach to develop future local climates The water resource quantity issuesdevelop various methods of downscaling that reflect large scale average features associated with the study area and theGCM simulations. They include and allows the use of all GCM and GHG headwaters of the Credit River includestatistical downscaling, weather emission scenarios. the following:generators, and regional climate models. • Future availability and reliability ofThe most established methodology for the percentile method municipal groundwater supplies;estimating future local climates uses the The iPCC recommends that waterGCM simulations to estimate annual, resource practitioners use as many • Baseflow/low flow concerns from aseasonal, or monthly changes for each future climate simulations as possible fisheries and wastewater assimilationclimate variable for a future time period when conducting a climate change perspective; and,relative to a baseline climate period. impact assessment. However, in most • High flow and peak flow concernsThese relative changes, called change assessments it is impractical to conduct from a flood risk and instream erosionfields, are used to adjust the observed an evaluation with the full set of over perspective. 60 future climateWhen assessing the impacts of simulations. The Guide The hydrology of the study area describes a method, is relatively complex. in addition toclimate change, understanding the referred to as the natural processes and sources of waterdistribution of streamflow throughout percentile method, for in the system there are several human selecting a smaller subset influences with significant consequences.a particular year is critical. of climate scenarios These influences include groundwater from the full list that is pumping for municipal supply,climate station data time series to reflect statistically representative of the full set. wastewater discharges into the Creditfuture conditions. This approach results Figure 1 illustrates a scatter plot of River, storage in a lake with controlledin an altered input climate time series GCM simulated annual mean change in outflow and the many incremental effectsthat reflects the average relative change temperature and precipitation for the of agricultural development, aggregatein each parameter and, through the use period of 2041 to 2070 for 57 scenarios extraction, and urbanization.20 WATER CANADA july/AuGuST 2011 WAT e R C A N A d A . N e T
  4. 4. ClimaTe Change Figure 3: Projected range of future mean monthly streamflow. the year. This seasonal shift is due to warmer air temperatures which lead to an earlier spring snowmelt. in addition, the majority of future climates will cause winter streamflow to experience increases of up to 50 per cent. increases in winter streamflow are primarily due to winter precipitation occurring predominantly as rainfall, rather than snowfall. Several scenarios estimate that summer low flows will range below current levels due to changes in summer precipitation and higher summer evapotranspiration in the future. Canadian water resource practitioners are going to be increasingly relied upon to make predictions of the impacts of climate change on our water resources. The Guide for Assessment of Hydrologic effects of Climate Change in Ontario describes an impact assessment To assess potential climate change basis over a 30-year period. To evaluate methodology that is suitable across all ofimpacts to streamflow and the water changes in streamflow, it is necessary Canada. While we cannot make definitebudget, the following tasks were to summarize long term hydrographs predictions of our future climate, thecompleted as set forth in the Guide: into statistical metric(s). examples state of climate change and hydrologic1 Selection of future climate datasets. of such statistical The selected climate change datasets metrics are mean included nine GCM scenarios selected annual and monthly Water resource practitioners are going using the percentiles method as well flow, median monthly as the baseline scenario. flow, maximum daily to be increasingly relied upon to make streamflow, and low2 development and calibration of a flows statistics, such as predictions of the impacts of climate physically based hydrologic model. Simulated parameters included 7Q streamflow. change on our water resources. When assessing the streamflow and water budget impacts of climate parameters (precipitation, runoff, change, understanding the distribution science is sufficient for our industry to recharge, and evapotranspiration) of streamflow throughout a particular estimate the likely range of impacts that3 development and calibration of a year is critical for a variety of water might be expected across Canada. With physically based MOdFlOW. The management aspects, including peak this information in hand we can begin to groundwater flow model utilized and low flow management, and fisheries identify potential impacts and suitable monthly groundwater recharge rates management. For this reason, changes mitigation and adaptation measures. WC as simulated by the hydrologic model. to monthly streamflow must also be4 Simulation of climate change impact investigated. scenarios. The hydrologic and Average monthly simulated streamflow hydrogeologic models were used to for the baseline climate and the nine simulate current conditions (1961 future climates are shown in Figure 3. Bob Walker is president of eBNlFO All nine future climates have streamflow environmental in Waterloo, to 1990) and nine separate future Ontario and is a specialist in water climate datasets for 2041 to 2070. distributions that follow a similar trend resources modelling and climate wherein flows peak in early spring, change impacts.5 evaluation of results. decline to annual lows through the The model simulations provide summer and rise through the fall and david van vliet is vice president of AquaResourcepredictions of runoff, evapotranspiration, early winter. However, the timing of inc., a specialized waterstreamflow, groundwater discharge, the decline in flow from the spring to resources consulting firmand water levels on an hourly or daily the summer is shifted to earlier in located in Waterloo, Ontario.22 WATER CANADA july/AuGuST 2011 WAT e R C A N A d A . N e T

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