watervulnerability

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