watervulnerability

Chequamegon-­‐Nicolet National Forest Watershed Vulnerability Assessment, Eastern Region (R9)
INTRODUCTION
Maintaining and restoring watershed resilience is an appropriate strategy for responding to climate change
because changes are anticipated to affect every component of the hydrologic cycle. But watersheds can
differ greatly in their vulnerability to climate change. Understanding differences in watershed
vulnerabilities is necessary to develop adaptive management strategies and implement targeted land
management practices.
Several National Forests, representing each region of the US Forest Service, are working to assess the
potential impacts of climate-induced hydrologic change on important water resources. Each forest is
identifying important water resources, assessing their exposure to climate change, evaluating risk,
categorizing watershed vulnerability, and recommending potential management responses.
The Chequamegon-Nicolet National Forest (CNNF) is one of the pilot Forests. This report summarizes an
assessment of watershed vulnerability associated with four important water resources: wetlands,
groundwater recharge, stream fishes and infrastructure (culverts at road stream crossings). More detailed
individual reports are available for each of these resource assessments.
These four resources were selected because of their importance to people and the local environment.
Wetlands (with an emphasis on bogs) were selected because of their importance to the northern
Wisconsin landscape and their apparent vulnerability to increased potential evapotranspiration.
Groundwater recharge was selected because of the importance of groundwater to the ecology of many
streams, lakes, and wetlands; the potential for changes associated with higher evapotranspiration; and to
take advantage of a groundwater inventory currently underway on the Forest. The ultimate goal will be to
model the projected effects of changes in groundwater recharge on aquifer levels, flow paths and flow
rates and to evaluate those effects on surface water resources. Wetlands and groundwater recharge were
also selected because they were unlikely to be addressed by the other National Forests in the pilot.
Infrastructure was selected because there is a concern that precipitation frequency and intensity may
increase in the future, threatening culverts that are not properly sized. This is one of the most urgent
management considerations because culverts installed now need to last up to 100 years. Stream fish-water
temperature was selected because of the potential for future stream temperature increases and the
subsequent effects on cold and cool water fish. It was also selected because there was an opportunity to
take advantage of a statewide analysis of the potential effects of climate change on stream fish in
Wisconsin.
METHODS
Methods are summarized here; more detail is provided in the following sections. In all cases, the
assessment included two basic steps: (1) some type of modeling to characterize the potential effect or risk
of projected climate change on the water resource, and (2) extrapolation of that potential risk to
characterize the vulnerability of that resource at the watershed scale. The five individual vulnerability
ratings (wetlands, groundwater recharge, infrastructure, cold water fish, and cool water fish) were
combined into one composite numerical watershed vulnerability ranking with the following thresholds:
1.0, very low; 1.2-2.4, low; 2.6-3.0, moderate; and 3.2-4.0, high. The composite rankings were based on
averages of the individual resource ratings.
Climate data required for modeling were obtained from the Wisconsin Initiative on Climate Change
Impacts (WICCI) program (www.wicci.wisc.edu/). The WICCI Climate Working Group has developed a
regional-scale, daily dataset of historical and future projections of total precipitation, and maximum and
minimum temperature for the time period 1950-2099 at an 8-km spatial resolution across Wisconsin. This
237 Assessing the Vulnerability of Watersheds to Climate Change