watervulnerability

Helena National Forest Watershed Vulnerability Assessment, Northern Region (R1)
climate variables assigned to each resource value. Lastly the sensitivity analysis outcome was overlaid
with the exposure analysis outcome to show final watershed vulnerability for each HUC-6.
Several different analysis units were used as part of this assessment. Sensitivity analysis was summarized
at the subwatershed level as delineated by the sixth level (12-digit) hydrologic unit (HUC-6) hierarchy in
the US Geological Survey (USGS) National Hydrography Dataset (NHD). Because many of the forest
management decisions and projects are conducted at the subwatershed scale or smaller, we chose to use
this scale to make this analysis most useful on the ground. This analysis includes 151 subwatersheds
within the assessment area.
The exposure analysis was conducted at the watershed scale (HUC-5) (Figure 2). This scale was used
because the climate data was downscaled to around a 6 km hydrologic output; this data fit our analysis
best at the HUC-5 watershed level.
To resolve these differences in scale, we used the sensitivity analysis at the subwatershed scale and
overlaid climate predications at the watershed scale to show how underlying subwatersheds may be
influenced by the climate predictions, while keeping the focus at a reasonable management scale.
Figure 2. HUC-6 subwatersheds and HUC-5 watersheds within Helena National Forest
WATER RESOURCE VALUES
The following water resource values were chosen for the vulnerability analysis. Although there are many
water resource values on the Helena National Forest, we analyzed the three values that we believe are of
greatest concern to the Forest.
48 Assessing the Vulnerability of Watersheds to Climate Change