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Chugach National Forest Watershed Vulnerability Assessment, Alaska Region (R10) Table 3. Predicted changes for annual mean precipitation in inches for the Eyak Lake and Resurrection Creek watersheds as a whole, and selected monthly totals for the towns of Cordova and Hope. Using data provided by SNAP, our GIS specialist determined the mean ordinal freeze and thaw dates, and from this we could derive the number of days where the average daily temperature was below freezing. The results do not appear to be consistent with other findings, since the B1 predictions suggest that conditions would be much warmer (later freeze and earlier thaw) than for the A1B scenario. Days Mean Temp < 0 °C Eyak Lake Resurrection Creek A1B Scenario B1 Scenario A1B Scenario B1 Scenario 2000-2009 91 76 165 166 2030-2039 62 27 152 99 2060-2069 21 34 118 74 Table 4. Predicted changes for the number of days below freezing for the Eyak Lake and Resurrection Creek watersheds as a whole General Area Climate Change Predictions Two other factors have the potential to exacerbate the effects of temperature and precipitation change: the predicted increase in extreme weather events and the accelerated melting of glaciers. Most sources agree about the trends, but it is difficult to predict the magnitude of these changes. It appears likely, though, that both will lead to increased stream flows, changes in sediment transport, and the potential for flooding. Extreme Weather Events Specific predictions for extreme weather events in the project area are not available. For high northern latitudes, however, Sillman and Roeckner (2008) state that there will be significant increases in the maximum and minimum temperatures and the amounts of precipitation for 5-day events and the 95 th percentile of wet days. They conclude that northern areas that have wet climates under the current conditions will become substantially wetter by the end of the 21 st century. Glacial Melting Site-specific conditions can greatly affect glacier formation or melting (Boggild et al. 1994, Dowdeswell et al. 1997, Arendt et al. 2010). Boggild et al. (1994) suggested that increased precipitation could add to glacial mass in Greenland, where there is an extensive higher-elevation land mass. Coastal Alaska has a number of high elevation glaciers as well. Topography, slope aspect, and local weather conditions, such as wind, can also affect accumulation of ice (Boggild et al. 1994). On the other hand, Crisitiello et al. (2010) found that the mass balance of two southeast Alaska glaciers has declined and has been correlated with temperature but not with precipitation. This suggests that increasing precipitation may not compensate for increased glacial melting. Closer to the project area, however, recent data indicate that most Alaskan glaciers are losing mass. Arendt et al. (2010) reported most of the 67 Alaskan glaciers surveyed during an early period from the 1950’s to the mid-1990’s, and 28 glaciers resurveyed from the mid 1990’s to 2001, had thinned. Less than 5% of the glaciers in the study had thickened, and most of these were tidewater glaciers where the melting of the toe of the glacier may have triggered other responses such as glacial surges (Arendt et al. 2010). They also found that during the latter period, when glaciers were resurveyed, the thinning rate was twice that of the earlier period. 276 Assessing the Vulnerability of Watersheds to Climate Change
Chugach National Forest Watershed Vulnerability Assessment, Alaska Region (R10) The glaciers that had thinned included the Scott Glacier that is adjacent to the Eyak Lake watershed and the Wolverine Glacier and Harding Icefield complex on the Kenai Peninsula, about 50 miles from the Resurrection Creek watershed. Thus, although we have no data for glacier or icefield melting within these watersheds, and cannot predict how increased precipitation might affect the mass balance, the recent trends suggest that there will be an eventual loss of glaciers. The predicted effects of glaciers melting are varied. Haufler et al. (2010) suggest that flows may initially increase with the additional meltwater, but that over time, the reduction in melting ice may cause streams to disappear. The higher meltwater flows may also erode unconsolidated glacial moraines, especially where glaciers have recently receded and the moraines are not vegetated. This could lead to increased sediment transport and eventual deposition in downstream areas. ASSESSMENT AREA RESULTS AND FINDINGS Eyak Lake Watershed Figure 4. Eyak Lake Watershed. The downstream delineation of the watershed is somewhat arbitrary as it is joined by the glacial Scott River to form an interwoven complex of channels before entering the Gulf of Alaska to the south. Area Description The primary reason for selecting the Eyak Lake watershed is that it is the most developed watershed of the eastern two-thirds of the Chugach National Forest. It also has the greatest range of aquatic resource values that might be affected by climate change. Predicted increases in air temperature, precipitation, and extreme weather events could result in damage to salmonid habitat, changes to salmonid life histories, 277 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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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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