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NF (Region 8) relied on information from The Nature Conservancy’s Climate Change Wizard (Table 2). The Chequamegon-Nicolet NF (Region 9) employed data from WICCI, and the Chugach NF (Region 10) utilized projections provided by the University of Alaska, Fairbanks (UAF) Scenarios Network for Alaska Planning Project (Figure 7). All the pilot assessments used air temperature change projections in their analyses and most pilots included projected changes to precipitation. These projections were obtained from the variety of publically available state or regional climate sources listed above. All projections of future climate are based on General Circulation Models (GCM). These models are mathematical representations of atmospheric and oceanic motion, physics, and chemistry, and employ different emission scenarios to yield predictions of temperature and precipitation change. The globalscale model outputs are very coarse, so data are often downscaled and used as inputs to macro-scale hydrologic models for use in regional and finer scale analysis, such as the WVA pilots. The accuracy of the data becomes more uncertain with each subsequent layer of modeling. The greatest certainty is associated with air temperature projections. Precipitation projections Projected Climatic Changes Anticipated Hydrologic Response Warmer air temperatures • Warmer water temperature in streams Changes in precipitation amounts and timing Less snowfall, earlier snowmelt, increased snowpack density Intensified storms, greater extremes of precipitation and wind • Altered timing and volume of runoff • Altered erosion rates • Higher winter flows • Lower summer flows • Earlier and smaller peak flows in spring • Greater likelihood of flooding • Increased erosion rates and sediment yields 10 | ASSESSING THE VULNERABILITY OF WATERSHEDS TO CLIMATE CHANGE are highly variable, with even less certainty for derived attributes like snowmelt, runoff, and stream baseflows. Precise changes in hydrologic extremes, such as flood and drought frequency, cannot be credibly modeled at the stream reach scale at present. The WVA pilot experience points to the value of broader scale (e.g., Regional) vulnerability analyses in providing exposure data and recommending future climate scenarios to National Forests. Interpreting exposure data at a broad scale would be useful for several reasons. First, exposure data is not available at finer scales. Second, consistency among National Forests in selected emissions scenarios and modeling assumptions would allow comparisons of expected climate changes across National Forests. Evaluating Hydrologic Changes Using projections of future temperatures and other climatic changes, most pilot Forests then considered what specific hydrologic changes would result from projected climate changes, and how water resource values would be affected by these changes. This step was integrative. In addition to the obvious connection Potential Consequences to Watershed Resources • Decrease in coldwater aquatic habitats • Increases or decreases in availability of water supplies • Complex changes in water quality related to flow and sediment changes • Changes in the amounts, quality and distribution of aquatic and riparian habitats and biota • Changes in aquatic and riparian habitats • Increased damage to roads, campgrounds, and other facilities Table 3. Projected hydrologic changes relative to identified values (Helena NF). Adapted from Water, Climate change, and Forests GTR (Furniss et al. 2010).
etween exposure and water resources, the evaluation served to stimulate thinking about which watershed characteristics might influence (either moderate or exacerbate) the hydrologic response to climate change, providing a segue to evaluating watershed sensitivity. An example of this type of analysis, which tracks climate changes through hydrologic responses to potential impacts on water resources from the Helena NF, is provided in Table 3. Applying Exposure Projections Once the hydrologic processes important to selected water resource values were identified, exposure metrics closely linked to those processes were identified. The list of metrics used to characterize exposure was limited because of the commonality in water resources in the assessments (Table 4). The selection of exposure metrics differed among National Forests for three reasons. The first is the water resources themselves. The Chequamegon-Nicolet was the only pilot Forest to include assessment of changes to groundwater recharge, and the only pilot Forest to use soil-water balance as an exposure metric. The second difference in selecting metrics was data availability. Both the Sawtooth NF and Umatilla NF assessments included finer-scaled analysis of potential changes to water temperature in evaluating change to bull trout habitat. These analyses were possible because of the availability of stream temperature data and predictive models, and the support of the Rocky Mountain Research Station (RMRS). The third difference in exposure metrics was the level of analysis. Differences in the depth of analysis were partly the result of data availability, as in the example described above. But the amount of time team leads could devote to the assessment was also a factor. Available time and perceived need for detailed analysis were practical National Forest Exposure Metrics Gallatin Combined flow, Snowpack vulnerability Helena Winter water temps, Summer air temps, Snow Water Equivalent (SWE), Precipitation GMUG Seasonal temperature, Aridity index Ouachita Monthly precipitation and Temperature White River Snowpack vulnerability Sawtooth Winter peak flows, Summer stream temperature, Summer flows Coconino Snowpack vulnerability Shasta-Trinity Air temperature, Stream aspect, Snowpack vulnerability Umatilla Winter and summer temperatures, SWE Chequamegon-Nicolet Air temperature, Precipitation, Soil water balance, Rainstorm frequency and intensity Chugach Air temperature, Precipitation, Freeze and thaw days Table 4. National Forests and metrics included to evaluate exposure effects in Water Vulnerability Assessments 11 | ASSESSING THE VULNERABILITY OF WATERSHEDS TO CLIMATE CHANGE Assessment Principle Four: Exposure Before Sensitivity The first iteration of the WVA process used in the pilot project called for assessment of sensitivity before evaluating exposure. The result was development of rather generic sensitivity factors that did not have the strongest links to hydrologic processes most likely to be affected by climate. Exposure is considered first in order to produce a list of the most important hydrologic changes affecting each water resource. Sensitivity elements that strongly modify these hydrologic changes are then selected. matters in the exposure analysis. Some pilots chose to make use of more detailed information that was available, and provided metrics with closer links to the subject water resources. Baseflow, for example, may be more closely linked with trout habitat than snowpack vulnerability but the decision to conduct more detailed analysis was largely driven by the anticipated need for adequate detail to rate watersheds and set priorities. Some analysts thought more detailed analysis would further discriminate areas at risk. Others thought the objective of rating watersheds could be met adequately with coarser evaluation of exposure. There are advantages and limitations to both the coarser and more detailed approaches to characterizing exposure. The common factor in cases where the most detailed analyses were conducted is that they evaluated effects on species which, because of population status and trend, were already the focal point of restoration strategies and management emphasis. In such cases, additional detail may be warranted. At the same time, exposure is the assessment component with the greatest
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Assessment of Watershed Vulnerabili
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Grand Mesa, Uncompahgre and Gunniso
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Coconino National Forest Watershed
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Chugach National Forest Watershed V
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