watervulnerability

Sawtooth National Forest Watershed Vulnerability Assessment, Intermountain Region (R4)
Current Low Risk Populations - By 2040,
three bull trout populations are still at low
risk, nine populations are at moderate, and
two are at high risk of extinction (Table 5
and Figure 16). Two populations at low
extinction risk (Germania and Upper Warm
Spring Creeks) have low risk from climate
change (i.e., frequency of winter peak flows
averaging 1.4 days, summer baseflows
averaging a 7% decrease, and summer water
temperatures changing very little). The other
low extinction risk population (Swimm-
Martin) is projected to have moderate
climate-change risks (i.e., frequency of
winter peak flows averaging 2.4 days,
summer baseflows averaging a 9% decrease,
and summer water temperatures changing
very little), but has good watershed that
should give the population enough resiliency
to withstand the predicted changes. By 2080,
all of these populations are predicted to be subjected to a greater frequency of winter peak flows (avg.
3.4), lower summer baseflows (avg. 28% decrease), and water temperatures outside optimal conditions
for bull trout in lower portions of each patch. However, only the Germania population goes to a moderate
risk of extinction from increasing effects of system roads in the headwaters and water diversions lower in
the drainage, due to climate change.
Current Moderate Risk Populations - Four populations (Big Boulder, Little Boulder, West Pass, and
Fourth of July Creeks) are at moderate risk more from current and historic management impacts and
moderate watershed conditions, than from climate change. This does not imply that there are no climate
change impacts predicted by 2040 within
these populations. There are still moderate
increases in winter peak flows (avg. 0.9 days),
and small changes to summer baseflows (avg.
8% decrease to 15% increase) and minor
water temperature increases. However, these
changes are not enough to increase extinction
risks. The remaining five bull trout
populations (Alturas Lake, Fishhook,
Prospect-Robinson Bar, Upper EF Salmon,
and Wickiup-Sheep) are projected to see a
greater frequency of winter peak flow events
(avg. 1.6 days), less baseflow (avg. 19%
decrease) and slightly warmer water
temperatures that may limit the use of habitat
Figure 17. Predicted bull trout persistence in 2080. Red
subwatersheds are at high extinction risk; yellow are at
moderate risk, and green are at low risk.
175 Assessing the Vulnerability of Watersheds to Climate Change
Figure 16. Predicted bull trout persistence in 2040. Red
subwatersheds are at high extinction risk; yellow are at moderate
risk, and green are at low risk.
during portions of the summer. By 2080
extinction risks increase to most of the above
bull trout populations as the frequency winter
peak flows and summer water temperatures
increase and summer baseflows continue to decrease (Figure 17). One additional local bull trout
population (Wickiup-Sheep) is projected to be at high risk; nine are predicted to be at moderate risk, and
two are predicted to be at low risk of extinction (Table 5).