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Assessment of Watershed Vulnerability to Climate Change Chugach National Forest March, 2012 Prepared By: Ken Hodges Fisheries Biologist Cordova Ranger District, Chugach National Forest Cordova, Alaska 266 Assessing the Vulnerability of Watersheds to Climate Change
SUMMARY This study was conducted as part of the USDA Forest Service Watershed Vulnerability Assessment Pilot Project. The goal of this study is to determine methods for assessing the vulnerability of aquatic resources to the predicted effects of climate change in the Chugach National Forest of southcentral Alaska. Many of the findings would also be applicable to coastal areas of southeast Alaska as well. The Chugach National Forest is somewhat exceptional in the National Forest system. Most of the Forest is undisturbed, with only 272 miles of road on 5.5 million acres, mainly state highways. There are no grazing allotments, no current commercial timber production to speak of, and limited active mineral extraction. Most of the Forest is managed for recreation and the conservation of fish and wildlife habitat. Climate change data were obtained from the University of Alaska, Fairbanks Scenarios Network for Alaska Planning program. Data are available online and some custom services were provided by the University. A review of the literature was conducted to determine how these changes are predicted to affect fish and wildlife, glaciers, and vegetation. Given that most of the watersheds in the Chugach are relatively pristine, ranking the vulnerability of all of the watersheds did not seem necessary. The large differences between ecosystem types were also not conducive to meaningful comparisons. Instead, two representative watersheds were selected for analysis: the Eyak Lake watershed near Cordova was chosen as representative of the coastal temperate rain forest ecosystem, and the Resurrection Creek watershed near Hope as more typical of the drier boreal forest of the Kenai Peninsula. Both watersheds are among the most developed on the Forest, although the overall disturbance may be considered low. Mean annual temperatures, precipitation, and days below freezing were developed for the watersheds by a Forest GIS specialist. Monthly data for Cordova and Hope, and other data are available online. Air temperature are predicted to increase in both areas, with summer temperatures increasing about 1.5 °C, but winter temperatures increasing about 4 °C. Precipitation is predicted to increase for all months in both watersheds, with a mean annual increase of 2 inches in the Resurrection Creek watershed and of 6 inches in the Eyak Lake watershed. All of these changes are well within the historic extremes. No predictions for extreme events in the future are available. Streamflow and water temperature data are limited in much of Alaska, and for the remote parts of the Chugach in particular. There are some stream gauge data for Resurrection Creek and Power Creek, which flows into Eyak Lake; however, the number of years of data are limited. I am unaware of VIC or other models that can be used to predict future flows with the available climate change data. Modeling flows is also complicated by conflicting factors. Snowpacks at lower elevations may be reduced by warmer temperatures in the fall and early spring, but this may be offset by higher precipitation and more snow at higher elevations. In addition, increased glacial melting may augment flows in late summer, which may compensate for an earlier melting of the snowpack – at least until the glaciers are gone. Given this complexity and limitations on the availability of modeling expertise, future conditions were judged qualitatively for each watershed. The assessment focused on the resource values in the watersheds, and particularly on the actions that could be taken to mitigate the predicted effects. Increased precipitation and the greater risk of rain-onsnow events make flooding and its effect on salmon habitat one of the greatest threats in both watersheds. Maintaining floodplain connectivity in the Eyak Lake watershed and restoring connectivity in the Resurrection Creek watershed are seen as the two most important mitigation measures to reduce the risks of salmon redd scour and other habitat damage. Increased erosion caused by higher precipitation, snow 267 Assessing the Vulnerability of Watersheds to Climate Change
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AUTHORS AND CONTRIBUTORS Authors* M
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ASSESSSING THE VULNERABILITY OF WAT
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staff; the task group included repr
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Figure 2. Conceptual model for asse
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Figure 3. Density of springs and sm
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Using Historic Data One finding con
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NF (Region 8) relied on information
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level of uncertainty. Though there
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climate (Casola et al. 2005). Only
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sensitivity. Most were derived from
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The sensitivity evaluation typicall
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in exposure. The result of combinin
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highest priority for management act
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to information affected the assessm
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with and rely on in many resource d
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Pilot National Forest Reports Conte
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Assessment of Watershed Vulnerabili
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Gallatin National Forest Watershed
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Helena National Forest Watershed Vu
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Grand Mesa, Uncompahgre and Gunniso
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White River National Forest Watersh
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Coconino National Forest Watershed
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Sawtooth National Forest Watershed
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Shasta Trinity National Forest Wate
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Umatilla National Forest Watershed
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Umatilla National Forest Watershed
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