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Sawtooth National Forest Watershed Vulnerability Assessment, Intermountain Region (R4) CLIMATE CHANGE EXPOSURE MODELS Water Temperature Potential effects of increased water temperatures due to climate change to bull trout were evaluated using a non-spatial multiple regression stream temperature model (Isaak et al. 2010). This model was created using an extensive, but non-random database of stream temperature measurements within the upper Salmon River, Upper S.F. Payette and Upper S.F. Boise subbasins on the SNF. More than 450 temperature measurements (Hobo and Tidbit models) were used from numerous resource agencies from 1994–2008. The majority of thermographs were placed in streams before mid-July, geo-referenced, and retrieved after mid-September. This sample period encompassed the warmest portion of the year when variation in temperatures among areas is most pronounced and influence on fish growth, behavior, and distribution is potentially greatest (Scarnecchia and Bergersen 1987, Royer and Minshall 1997). Predictor variables (i.e., geomorphic, climatic, and categorical) were used to describe spatial and temporal attributes associated with the stream network. Geomorphic predictors included watershed contributing area, elevation, and channel slope. Predictors in this category represented relatively static features of the river network, valley bottoms, and upstream watersheds that were hypothesized to affect stream temperatures. Interannual variation in climatically-influenced factors such as air temperature and stream flow have important consequences for stream temperatures. Air temperature affects stream temperature through sensible heat exchange near the surface of the stream and by influencing temperatures of near surface groundwater, which is an important component of summer flows. Stream flow determines the volume of water available for heating; larger flows have greater thermal capacities and are less responsive to heating (Hockey et al. 1982, Caissie 2006). Climate predictors included air temperature measurements derived from extrapolations of the observed 30 year trends at cooperative weather stations (Ketchum and Stanley) on the Sawtooth National Forest, and the 50 year trends at the USGS gauges (S.F. Boise River near Featherville, S.F. Payette River at Lowman, and Salmon River below Yankee Fork near Clayton) with the longest records on or near the SNF. The air temperature data between weather stations was strongly correlated (r 2 = 0.74–0.91), so the individual time series were averaged and the same summary metrics that were applied to model stream temperatures were applied (i.e., MWMT). Flow data were obtained from two USGS stream gauges in the basin (Twin Springs and Featherville gauges). These two sets of data were also strongly correlated (r 2 = 0.97) and were averaged to calculate annual mean flow (m 3 /s) from 15 July to 15 September. Air temperature projections, used in the water temperature model, assume climate change will continue at the same rate that has occurred in the last 50 years on the forest. This likely underestimates the amount of change (as predicted by or some IPCC climate change scenarios). These scenarios generally predict the rate of air temperature change to accelerate due to increased carbon dioxide (Isaak/Wegner, pers. comm.). The advantage of using empirical estimates is that they're based on data from the Forest, are easy to understand. They provide estimates comparable to those from the IPCC scenarios for future values at mid-century. Categorical predictors included effects due to increased water temperature in lake outflows, water diversions, wildfires, and professional judgment. All upstream wildfires that occurred within the past 20 years were considered. Water diversion effects on water temperatures were coded from zero (when they diverted less than 5% of flow) to three (when they diverted more than 30% of flow). Diversion effects on stream temperature were assumed to extend as far as 7 km downstream of the diversion or to a confluence with a larger river or stream. Finally, lakes larger than 0.1 km 2, or groups of lakes, were considered to 166 Assessing the Vulnerability of Watersheds to Climate Change
Sawtooth National Forest Watershed Vulnerability Assessment, Intermountain Region (R4) have an influence on water temperatures as far as 7 km downstream or to the confluence with another water body. All predictors were found to be significant (p
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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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Umatilla National Forest Watershed
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Ouachita National Forest Watershed
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Chugach National Forest Watershed V
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