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Chequamegon-­‐Nicolet National Forest Watershed Vulnerability Assessment, Eastern Region (R9)<br />

data is available for 14 global circulation models (GCMs) and three future scenarios for greenhouse gas<br />

emissions (A2, A1B, B1). It was developed by downscaling the coarse-scale climate projections of the<br />

GCMs. The ideal approach for climate change analyses would be to model the effects for all 14 GCMs<br />

and all three scenarios to evaluate the full range of potential climate change impacts. Given limited time<br />

and resources, this assessment used just one GCM, the GFDL-CM2.0, and one scenario for one pixel of<br />

data located on the Park Falls unit of the CNNF. The A1B scenario was selected because it provides an<br />

intermediate level of greenhouse gas emissions relative to the other scenarios.<br />

Wetlands<br />

Potential changes in wetland hydrology were determined using the Peatland Hydrologic Impact Model<br />

(PHIM) (Guertin et al. 1987; Brooks et al. 1995). PHIM is a physically-based, continuous simulation<br />

model for predicting water yield and streamflow from peatland and upland watersheds typical of the<br />

northern Great Lakes region.<br />

The PHIM was run with 40 years of historic climate data (1961-2000) and 20 years of projected climate<br />

data (2046-2065). The potential effect of climate change on bog hydrology was evaluated by determining<br />

differences in average annual and seasonal runoff and evaporation from the upland-peatland complex, and<br />

average annual and seasonal water level in the bog. The results were extrapolated to all HUC-6<br />

watersheds encompassing the National Forest based on the proportion of total wetland and acid wetland<br />

in each HUC-6 watershed.<br />

Groundwater Recharge<br />

The groundwater recharge portion of the analysis focused on the Park Falls unit of the Forest to take<br />

advantage of a recently initiated project characterizing groundwater resources on this portion of the<br />

Forest. This project is being conducted by the Wisconsin Geological and Natural History Survey<br />

(WGNHS) and United States Geological Survey (USGS).<br />

Potential changes in groundwater recharge were determined for the Park Falls unit using the Soil Water<br />

Balance Model (SWBM) (Westenbroek et al. 2010; Dripps and Bradbury 2007). The SWBM estimates<br />

recharge using gridded watershed data and tabular climatic data. The watershed data include soil water<br />

capacity, hydrologic soil group (HSG), flow direction, and land use.<br />

The results of the Park Falls modeling were extrapolated to all HUC-6s encompassing the National Forest<br />

based on the proportion of HSG in each HUC-6. Watersheds with no or reduced recharge were considered<br />

most vulnerable while those with increases in recharge were considered least vulnerable or most resilient.<br />

Infrastructure-Culverts<br />

The analysis included four primary steps: (1) evaluating climate change projections to determine the<br />

potential for increases in flood magnitudes, (2) reviewing culvert sizing criteria and hydraulic modeling<br />

results, (3) determining road-stream crossing density and runoff potential for HUC-6s within the CNNF,<br />

and (4) characterizing the vulnerability of HUC-6s to increased flood flows and failure of culvert<br />

infrastructure based on steps 1-3.<br />

WICCI summary data were evaluated for evidence that flood flows may increase in the future. Key data<br />

used for this evaluation were projections for the frequency of 1-, 2-, and 3-inch rainstorms and for annual<br />

and seasonal precipitation and air temperatures.<br />

238 Assessing the Vulnerability of Watersheds to Climate Change

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