Watershed Management and Climate Change
Since then, its definition has expanded: first from a focus on flood control and erosion to one which includes broader terrestrial and aquatic environments, and more recently to include social issues related to the use of the natural environment, making watershed management one of the most inclusive ecosystem-based management frameworks, developed to date. Now, it must expand again to address Climate Change, and must do so with respect to natural science, mitigation, and adaptation, terms which will be explained in more detail below.
Managing on an ecosystem basis involves the recognition that all components of the natural hydrologic system are interconnected to the extent that changes to one component often are reflected in significant impacts or alterations to the other ecological components. An example of this fact is quite apparent when we look at the changes which have been occurring within watersheds with increased urbanization.
In the 1970's, it was recognized that urban land forms removed permeable areas and replaced them with impermeable surfaces, thus generating a higher volume of water. This increase in volume was being characterized as increased surface runoff, less evapotranspiration, less surface depression storage and therefore less infiltration. The overall consequences of this land form change has been increased flooding and erosion along receiving streams.
Early attempts to deal with the increased volume of water within our rivers and streams was centered around stormwater management by shaving peak flows to try and match post development peak flows to pre-development levels. While this practice is now commonplace, it falls short of dealing with all the impacts of urbanization. Higher flow volumes and peaks create erosion along the watercourses, resulting in significant impacts to infrastructure and to the form and function of the aquatic habitats.
In addition, water quality has been degraded to the point that many streams now support a significantly different, or much reduced fishery. The change in the aquatic environments has now begun to affect both the flora and fauna that exists within our valley systems. While new initiatives have been introduced that attempt to reduce the impacts on the natural systems through development, changes continue to occur as a consequence of past and current actions. For instance, upon completion of a watershed becoming urban, the impacted watercourse may require between 35-200 years before adjusting to its revised flow regime depending on flow channel soil conditions.
Current initiatives and strategies of Watershed Management hinge on working in concert with the dynamic aspects of the natural environment and its features. The development of strategies related to natural heritage features on a watershed allow for an integration of flexibility and evolution within the system. As such, the concept of management on a watershed is based to some degree on the ability to manage and plan within the system, while allowing natural processes and changes to continue to take place. The watershed and its current management objectives, therefore, inherently allow for some degree of adaptation related to the potential impacts of climate change.
Traditional management of watersheds from an aquatic perspective has centered around mitigating impacts related to land use change for the portions of the hydrologic cycle where precipitation moves over the landform to the receiving watercourses. Climate change will bring changes to the atmospheric components of the cycle. Changes in evaporation rates, severity of storms, increased temperatures and droughts created through climate changes may result in significant alterations within the natural ecosystem of a watershed. These changes for example, may impact everything from species diversity, to habitat health, to human communities - particularly how communities interact with and within the natural ecosystem.
Current initiatives to deal with climate change are focused on reducing our loadings of greenhouse gasses into the atmosphere. Due to global economic and technical capabilities, these loadings may not be eliminated in the foreseeable future. In addition, carbon dioxide has a residency time of near 90 years aggravating the existing problem. We can expect that GHGs will continue to increase, reaching levels over the next 50-70 years that are double those of pre-industrial times. As a result, the climate of the Great Lakes Basin is expected to change dramatically within this period. Climate change may provide some advantages and opportunities, as long as measures are taken to realize the potential benefits. The Toronto region's success in responding to these challenges will hinge on the ability and willingness to effectively incorporate climate impacts and adaptation into the planning processes. Given the size of this region's population and industrial base, our actions will also be crucial to Canada's success in achieving its greenhouse gas reduction targets under the Kyoto Protocol.
(Haley and Auld, 2000)
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Integration Of ClimateChange Into Watershed Management - 72K 
Reference:
Auld, H. and Haley, D. 2000. Integration of Climate Change Into Watershed Management. From proceedings of CWRA Ontario Water Conference, Challenges and Solutions, Richmond Hill, April 26-27 of 2000.
