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Chugach National Forest Watershed Vulnerability Assessment, Alaska Region (R10) ASSESSMENT AREA DATA Assessment Areas • Eyak Lake watershed – coastal rainforest ecotype • Resurrection Creek watershed – drier boreal forest ecotype Of the 85 fifth level HUCs and 275 sixth level HUCs on the Forest, only a handful have significant development, infrastructure, or active land management. The two watersheds used for this assessment have the widest variety of development and aquatic resource values for their respective ecotypes and can serve as representative watersheds for many coastal Alaska areas. The Eyak Lake watershed contains part of Cordova, a small city of 2,440 people. The town of Hope (182 residents) is adjacent to the lower part of the Resurrection Creek watershed. Eyak Lake Resurrection Creek Area (acres) 27,748 103,215 HUC Level Two 6 th levels 5 th level w/ three 6 th National Forest Land 25,554 (92.1%) 100,839 (97.3%) Mean Annual Air Temperature July January 5.3 °C 12.5 - 4.1 Water Temperature Summer surface Eyak Lake 5.5 - 14.5 °C Power Creek mean 6.1°C annual 3.0 - 8.4 °C Mean Discharge (cfs) 387 (ungauged) 10-yr Flood 8,700 274 Assessing the Vulnerability of Watersheds to Climate Change 2.6 °C 14.1 - 7.2 Resurrection Creek Mean 8.4 °C Range 5.5 -12.0 °C 275 2,400 Mean Precipitation (inches) 130.25 22.15 Lake/Pond Area (acres) 2,400 (8.6%) 80.5 (0.07%) Road Density - mile/mile 2 (total) 0.36 (25.1) 0.14 (35.1) Residential/Commercial Area (acres) 205.3 (0.7%) 53.1 (0.05%) Area Unvegetated Rock (acres) (%) 5,405 (19.7%) 11,391 (11.0%) Area Icefields/Glacier (acres) (%) 3,256 (11.7%) 245 (0.2%) Area > 70% Slope (acres) (%) 6,332 (23.1%) 7,660 (7.4%) Avalanche Area (58-173% slope) (acres) (%) 12,001 (43.7%) 20,952 (20.3%) Area > 500 ft Elevation (acres) (%) 20.553 (74.0%) 100,324 (97.2%) Fire, Including Prescribed Burns (acres) (%) 0 9,400 (9.1%) Mining Disturbance (acres) (%) 0 2,560 (2.5%) Trails (miles) 13.1 16.8 Recreation Sites (cabins, camps, day use) 5 14 Table 1. Current conditions for the Eyak Lake and Resurrection Creek watersheds. Assessment Area Climate Change Predictions The general predictions for both the Eyak Lake watershed and the Resurrection Creek watershed call for increased temperatures. Annual mean temperatures are predicted to increase 1.7 to 1.9 °C for the two watersheds under both the A1B and B1 scenarios (Table 2). However, winter temperatures are predicted to increase much more than summer temperatures. Monthly data for the entire watersheds were not readily available, but the January temperatures for the towns of Cordova and Hope are predicted to rise 3.4 to 3.7 °C, and the July temperatures 1.5 to 1.8 °C.
Chugach National Forest Watershed Vulnerability Assessment, Alaska Region (R10) Eyak Lake Resurrection Creek Air Temperature °C Annual Mean Annual Mean A1B Scenario B1 Scenario A1B Scenario B1 Scenario 2000-2009 4.3 3.5 1.4 0.5 2020-2029 5.1 4.4 2.1 2.1 2050-2059 6.1 5.3 3.1 2.4 Cordova January Hope January 2001-2010 -1.4 -3.3 -6.1 -8.2 2031-2040 -0.2 0.7 -5.2 -4.2 2061-2070 2.3 0.2 -2.3 -4.7 Cordova July Hope July 2001-2010 14.1 13.1 15.1 14.1 2031-2040 14.3 14.4 15.2 15.4 2061-2070 15.6 14.9 16.7 15.9 Table 2. Predicted changes for annual mean air temperatures for the Eyak Lake and Resurrection Creek watersheds as a whole, and selected monthly temperatures for the towns of Cordova and Hope. Annual mean precipitation is generally predicted to increase, although the total amounts are quite different for the two watersheds. As shown in Table 3, the increase in the Eyak Lake watershed as a whole is predicted to be as much as 6.7 inches under the A1B scenario, while the Resurrection Creek watershed may see an increase of 3.1 inches. The data for the driest and wettest months for Cordova and Hope were taken from the SNAP community charts (2011), and generally show small increases over time. Unlike the other trends, the prediction for June 2061-2070 shows a slight decrease, but given the variability among the models used for the prediction (University of Alaska, Fairbanks 2011), this is probably not significant. It should also be mentioned that the historic annual precipitation levels are highly variable for the Cordova area. The Cordova airport weather station, which is about 10 km from the Eyak Lake watershed, has an annual mean of 96.26 inches, but a historic range of 54.41 to 139.34 inches. Thus, while an average annual increase of six inches will lead to higher flows and presumably more extreme events, the watershed already experiences extreme changes. This makes it difficult to determine how, or how much, geophysical and biological conditions will be affected. From 1979 to 1995, a low-elevation station near Hope had a precipitation range of 15.19 to 31.30 inches, with a mean of 22.15 (Kalli and Blanchet 2001). The predicted amounts for the entire watershed are higher as shown below, but the predicted changes still appear well within the historic range. Eyak Lake Resurrection Creek Precipitation Inches Annual Mean Annual Mean A1B Scenario B1 Scenario A1B Scenario B1 Scenario 2000-2009 177.2 176.9 34.5 38.0 2020-2029 179.6 178.3 35.8 38.1 2050-2059 183.9 179.0 37.6 39.8 Cordova June Hope May 2001-2010 7.81 7.52 0.85 0.89 2031-2040 7.86 7.50 1.05 0.96 2061-2070 7.70 7.69 1.14 1.01 Cordova October Hope September 2001-2010 21.13 20.83 3.52 3.73 2031-2040 21.92 21.19 3.68 3.50 2061-2070 22.10 21.23 4.47 3.97 275 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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Page 228 and 229: Umatilla National Forest Watershed
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