watervulnerability

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).