Citation | Little, P. 2012. Theodosia Watershed: Climate Change Impacts and Adaptation Plan. Prepared for Theodosia Stewardship Roundtable. |
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Organization | Living Rivers - Georgia Basin/Vancouver Island |
URL | http://www.fraserbasin.bc.ca/_Library/CCAQ_BCRAC/bcrac_theodosia_watershed_plan_2d.pdf |
Abstract/Description or Keywords | The Theodosia watershed is a 140 km2 coastal basin situated approximately 30 km north of Powell River. Land and water use in the watershed includes forestry and diversion of water for hydroelectricity. Well over half of the basin area has been harvested at least once and the diversion extracts over 60% of the water from the upper Theodosia River. The river supports substantial populations of Chum and Coho salmon, which have severely declined since the early 1950s, and provides habitat for several other salmonids. Increased CO2 concentration in the earth’s atmosphere is resulting in several changes to the climate and hydrology of the Theodosia watershed. Summers are projected to become dryer and hotter with more frequent heat waves and increased year-to-year variability compared to historical levels. Winters will likely be warmer and wetter. Large and frequent winter rainstorms and a large decrease in snowfall at all elevations in the watershed should be expected. Changes in climate will result in changes in the hydrology of the Theodosia River. Reduced snowpack will result in a shift in timing of streamflow to earlier and diminished spring peak flows. By the middle of the 21st century, it is likely that very little snowpack will be left to contribute to spring streamflow. Furthermore, reduced snowfall, decreased summer precipitation, and increased temperatures will likely result in lower summer/fall stream flow and more extreme low flow periods. The river will also likely experience increases in the frequency and magnitude of fall and winter flood events. Increased stream temperature at all times of year should also be expected. Climate change will impact stream habitat and salmonids in several ways. The greatest impacts will likely come from increased frequency and magnitude of winter floods that will increase scouring and burial of both Coho and Chum salmon eggs. Lower summer and early fall streamflow will also be detrimental to fish populations, as will possible complex interactions due to mismatched timing of predator/prey interactions or mismatched life history stages with the hydrologic regime. Chum salmon may be able to better adapt to the future climate regime than Coho although yet unknown complex interactions add uncertainty to this statement. Impacts to forest resources may be less severe than impacts to fisheries, with the most common impact being lower growth rates. However, it is possible that large-scale disturbances due to fire and/or insect/disease outbreaks may have severe consequences to the forests of the watershed. The likelihood of such impacts is very difficult to predict. The final chapter of this document outlines several adaptation strategies that may serve to increase the resilience of ecosystems in the watershed. The Theodosia Stewardship Roundtable (TSR) must work to enhance the lines of communication between stakeholders and to develop shared decision making protocols in the face of climate change. A water use plan for the Olsen Lake diversion should be created and future infrastructure should reflect this plan. It is recommended that water extraction during the summer is decreased to mitigate effects of drought, while water use during the winter is managed to mitigate impacts of peak flows in the lower watershed. Forest companies and the BC Ministry of Forests, Lands and Natural Resource Operations should work with the TSR to develop a coordinated watershed-scale sustainable harvesting plan that details targeted harvest rates, new protocols for culvert sizing, and plans for restoration and conservation of floodplain forests. Flood risk, landslide risk and risk of storm surge due to sea level rise will increase in the lower floodplain area; thus, future settlement plans will require professional surveying to avoid locating buildings in high-risk areas. |
Information Type | report |
Regional Watershed | Howe Sound & Sunshine Coast |
Sub-watershed if known | Theodosia |
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