watervulnerability

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