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Chugach National Forest Watershed Vulnerability Assessment, Alaska Region (R10) areas, there is likely a need to collect simple baseline data, such as groundwater temperatures, that can be monitored over time to detect or verify predicted changes. Most of all, managers need to determine how the information is going to help make on-the-ground decisions. Certainly, we would like to know that if fry develop faster and emerge earlier, their food resources will also develop faster and will be available. But we need to be thinking about how we can mitigate the situation if necessary. And this isn’t necessarily building enhancement structures or replacing culverts. New information can be used to justify policies and management, such as a reduction in salmon harvests or other conservation measures. The main point is that the complexity of climate change is bringing up lots of questions, and managers would do well to establish specific needs and research priorities before getting started. CRITIQUE General Approach The initial steps that were suggested for this assessment follow a rational and logical progression – defining the assessment area, identifying the resource values, describing the sensitivity of these values, identifying stressors, and determining exposure. Identifying the resource values is especially important because it focuses the analysis on the relevant issues. The other Forests compared all of their watersheds to determine which were the most vulnerable but this was not a priority for the Chugach. As mentioned earlier, most of the watersheds have little or no development – 99% of the Forest is in roadless areas. Although climate change can affect resources in all of the watersheds, I felt that it was unlikely that managers would conduct mitigation measures in pristine areas. Not ranking the relative vulnerability of the watersheds may be one weakness of this assessment. The assessment does not show, for example, that the fisheries values of the Kenai River system (with headwaters on National Forest land) far outweigh the Resurrection Creek fisheries. However, Chugach managers don’t have more than a half dozen developed watersheds to look at, so they have the luxury of being able to look closely at each watershed. Given the low levels of development in the Kenai area and knowing that the climate change conditions will be similar, managers will still need to be working on a site-specific scale, watershed by watershed, to develop meaningful plans and establish project priorities. Data Availability There is a good deal of climate change information available from the UAF SNAP program, from raw GCM data to ready-made maps and graphs. Other websites have historic evapotranspiration estimates and other parameters that could be useful in more extensive analyses. Predicting change for streamflow and runoff timing in coastal Alaska is difficult due to several conflicting factors. Climate change models predict warmer temperatures and increased precipitation for coastal Alaska, but given the high elevations of the area, reductions in snowpack at lower elevations may be offset by higher precipitation and more snow at higher elevations. Earlier melting of the snowpack may be compensated for by increased glacial melting augmenting flows in late summer, – at least until the glaciers are gone. Most of the literature agreed that glaciers were melting more rapidly, but increased snowpacks in coastal Alaskan mountains was only mentioned as a possibility. 298 Assessing the Vulnerability of Watersheds to Climate Change
Chugach National Forest Watershed Vulnerability Assessment, Alaska Region (R10) As a result, the main data gap was an estimate of the future change in streamflows, snowpacks, runoff timing, and other parameters. My assumption is that this information is available from VIC and other models for the lower 48 states, but I am not aware that such data are available for Alaska yet. The limited numbers of stream-gauging stations, limited duration of station operation, and the limited number of weather data sites in remote areas may be part of the reason. In any case, the data did not appear to be readily available, so I turned my focus to qualitative assessments. Other data gaps included long-term water temperature data and stream height/flood level data. Having more specific data would have added more certainty to some statements and conclusions, but overall I think the general concepts are valid. The accuracy of the data provided by the models appeared to be a little questionable at times. For some areas near Cordova, the maps don’t always fit the topography, which may reflect the extrapolations between distant weather stations or distance from the ocean. The 2 km cells may also add some uncertainty if one is trying to analyze a relatively small area. However, if one is only looking for trends, small discrepancies may not be a concern. The variation among models also raises some questions. The SNAP website states that the variability among the models is generally in the range of 0-4 °F and 0-0.7 inches for precipitation. Four degrees is a large range when one is looking at winter temperatures that are near freezing. For Hope, where conditions are relatively dry, the range of variability for precipitation is often greater. There is also the question of whether an average of five models is any more accurate than any single model. Thus, if one were to do a quantitative analysis, there may be problems. However, the models all agree in the general trends, which should be sufficient for some types of analysis. Assessing Risk One of the suggested methods for assessing overall watershed vulnerability was to create a risk matrix, comparing various attributes such as road density or slope, values such as fish populations, predicted climate change parameters, and then assign risk levels on a low to high scale. The total scores would be used to determine the most vulnerable watersheds. This process did not appear to be applicable for the Chugach National Forest, where most of the watersheds are undisturbed, road densities are uniformly low or zero, and the risks to fish and other wildlife from the predicted climate changes are unclear. Assigning different levels of risk seemed to be subjective, given the wide differences between the ecosystems. While winter temperatures are expected to increase by about 3.7 °C for both Hope and Cordova, the effect in Cordova will be much greater since low-elevation winter temperatures are hovering around the freezing point. Similarly, larger precipitation increases in Cordova are probably less meaningful, given the currently high precipitation. Also, some watersheds may have greater fire hazards, while others may have more valuable fish, so the comparisons may not be equal. With the limited number of developed watersheds, it didn’t seem necessary to rank them to determine which are the most vulnerable. For the Chugach, it seems simpler to identify the specific issues for each watershed on its own, since there are only a few to analyze. The other problem is determining the magnitude of adverse effects from climate change over existing conditions. As discussed, the predicted increases in temperature and precipitation are well within the historical variability, although more extreme weather events are expected. While one can intuitively say that greater precipitation could lead to greater erosion and landslides, it may be difficult to argue that another 6 inches of rain will increase landslides in a watershed that already receives a mean of 177 inches. 299 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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Grand Mesa, Uncompahgre and Gunniso
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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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Ouachita National Forest Watershed
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Chequamegon-‐Nicolet National F
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