Biological Opinions - Bureau of Reclamation

inches (15.24 cm) during March, April, and May in the southern Oregon Cascades for the 50-
year period evaluated. A decline of 6 inches (15.24 cm) equals an approximate 20 percent
reduction in snow water equivalent. Declines in snowpack are expected to continue in the
Klamath basin.
Recent winter temperatures are as warm as or warmer than at any time during the last 80 to 100
years (Mayer 2008). Air temperatures over the region have increased by about 1.8º to 3.6º F (1°
to 2º C) over the past 50 years and water temperatures in the Klamath River and some tributaries
have also been increasing (Bartholow 2005; Flint and Flint 2012). Reclamation (2011a) reports
that the mean annual temperature in Jackson and Klamath Counties, Oregon, and Siskiyou
County, California, increased by slightly less than 1 °C between 1970 and 2010. During the
same period, total precipitation for the same counties decreased by approximately 2 inches (5.08
cm; Reclamation 2011a).
Analysis of climatologic and hydrologic information for the upper Klamath Basin indicates
Upper Klamath Lake inflows, particularly base-flows, have declined over the last several
decades (Mayer and Naman 2011). Recent analyses completed for this BiOp confirm the trend
in declining inflow to Upper Klamath Lake and also demonstrate declining flows in the
Williamson and Sprague rivers (major tributaries to Upper Klamath Lake) from 1981 through
2012. Net inflow to Upper Klamath Lake and flow in the Williamson and Sprague rivers are
strongly dependent on climate, particularly precipitation (Mayer and Naman 2011). Part of the
decline in flow is explained by changing patterns in precipitation; however, other factors are very
likely involved as well, including increasing temperature, decreasing snow water equivalent,
increasing evapotranspiration, or possible increasing surface water diversions or groundwater
pumping upstream of the lake (Mayer 2008; Mayer and Naman 2011).
Projections of the effects of climate change in the Klamath Basin suggest temperature will
increase in comparison to 1961 through 2000 time period (Barr et al. 2010; Reclamation 2011a).
Projections are based on ensemble forecasts from several global climate models and carbon
emissions scenarios. Although none of the projections include data for the specific period of the
proposed action, anticipated temperature increases during the 2020s compared to the 1990s range
from 0.9 to 1.4° F (0.5 to 0.8° C) (Reclamation 2011a).
Effects of climate change on precipitation are more difficult to project and models used for the
Klamath Basin suggest decreases and increases. During the 2020s, Reclamation (2011a) projects
an annual increase in precipitation of approximately 3 percent compared to the 1990s.
Reclamation (2011a) also suggests that an increase in evapotranspiration will likely offset the
increase in precipitation.
Reclamation (2011a) projects that snow water equivalent during the 2020s will decrease
throughout most of the Klamath Basin, often dramatically, from values in the 1990s. Projections
suggest that snow water equivalent will decrease 20 to 50 percent in the high plateau areas of the
upper basin, including the Williamson River drainage. Snow water equivalent is expected to
decrease by 50 to 100 percent in the Sprague River basin and in the vicinity of Klamath Falls. In
the lower Klamath Basin, Reclamation projects decreases in snow water equivalent between 20
and 100 percent. The exception to the declines is the southern Oregon Cascade Mountains,
245