watervulnerability
watervulnerability
watervulnerability
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Chugach National Forest Watershed Vulnerability Assessment, Alaska Region (R10)<br />
This assessment was made based on the conditions of the Chugach National Forest along the southcentral<br />
coast of Alaska, but it could be applicable to other areas in coastal Alaska, including southeast Alaska.<br />
The intent of focusing on just two watersheds is to have them serve as examples for land managers who<br />
may have watersheds with similar issues.<br />
METHODS<br />
The directions that participants in this pilot project were given included a number of practical steps. These<br />
included:<br />
• Describing the assessment areas, existing conditions, and the major water resources, or the waterrelated<br />
values or benefits in these areas.<br />
• Determining the anticipated climate change and its degree, using various predictive climate<br />
models.<br />
• Describing the predicted changes to hydrologic processes.<br />
• Determining the effects on water resources or values.<br />
• Describing the conditions that might amplify the changes and effects (stressors) or reduce them<br />
(buffers).<br />
• Determining the degree of watershed risk.<br />
• Describing how the findings might be applied to management activities at various geographic<br />
levels.<br />
The initial steps required consultations with area managers, literature searches (particularly of the gray<br />
literature), collecting historic temperature and precipitation data, and determining the availability of site<br />
specific data such as stream flows or water temperatures.<br />
The University of Alaska, Fairbanks (UAF), in collaboration with government agencies and nongovernmental<br />
organizations, conducts the Scenarios Network for Alaska Planning project (SNAP), which<br />
provides climate change data using a variety of Global Circulation Models (GCM) linked with historic<br />
Parameter-elevation Regressions on Independent Slope Models (PRISM) data. The resulting SNAP data<br />
can then make climate change predictions based on historic data that also take into account elevation,<br />
topographic facet, coastal proximity, slope, and distance from weather stations. This is particularly<br />
important in Alaska where there are large areas with few or no stations.<br />
There are ready-made maps with 2 km cells available online for temperature and precipitation, but the<br />
scale increments are somewhat coarse: 3 °C for temperatures close to freezing and 50 mm increments for<br />
precipitation. However, these maps are sufficient to determine overall trends and a rough estimate of the<br />
amount of change. Analysis requires downloading the data.<br />
For the initial efforts, UAF provided me with GIS layers of the Eyak Lake watershed where I could<br />
manipulate the scales to better detect freezing points and finer changes in precipitation. Since the<br />
elevations range from near sea level to 4,600 ft, the temperatures and precipitation vary significantly over<br />
short distances. The data were an average of the five GCM’s that best matched historical data.<br />
After the project was expanded to include Resurrection Creek, a GIS specialist for the Chugach National<br />
Forest downloaded and manipulated additional data available from SNAP for both watersheds. By using<br />
the raw data for each 2 km cell, the GIS specialist was able to average and obtain mean values for the<br />
watersheds as a whole. This was done for annual mean temperatures, annual mean precipitation, the<br />
freeze day, and the thaw day. The freeze and thaw days are extrapolated predictions of when the average<br />
271 Assessing the Vulnerability of Watersheds to Climate Change