Biological Opinions - Bureau of Reclamation

(2011) projects an annual increase in precipitation of approximately 3 percent compared to the
1990s. Reclamation (2011) also suggests that an increase in evapotranspiration will likely offset
the increase in precipitation. In the 2035 and 2045 period, the change in annual precipitation
compared to the 1961 through 1990 is expected to range from approximately -9 percent to +3
percent (Barr et al. 2010). Within the boundaries of the annual change in precipitation,
December through February precipitation is expected to increase by up to 10 percent while June
through August precipitation is expected to decrease between 15 and 23 percent (Barr et al.
2010).
Reclamation (2011) 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,
where snow water equivalent is projected to be stable or increase up to 10 percent (U.S. Bureau
of Reclamation 2011).
Reclamation also projects annual increases in runoff during the 2020s compared to the 1990s,
based on the global climate models. The annual volume of flow in the Williamson River is
expected to increase by approximately 8 percent, with increases of approximately 22 percent
during December through March and decreases of approximately 3 percent during April through
July (Reclamation 2011). The Klamath River below Iron Gate Dam is expected to experience an
approximate 5 percent increase in annual flow volume, with increases of approximately 30
percent during December through March and decreases of approximately 7 percent during April
through July (Reclamation 2011).
The apparent contradiction between decreasing snow-water equivalent and increasing runoff is
resolved by projections suggesting a greater proportion of precipitation will fall as rain instead of
snow, and the increase in overall precipitation will be greater in the winter than in the summer.
The USGS has modeled potential responses to climate change in the Sprague River Basin using
several global climate models and carbon emissions scenarios (Markstrom et al. 2011, Risley et
al. 2012). The models simulated the effects of climate change between 2000 and 2100 compared
to a 12-year baseline period of water years 1988 through 1999. The results indicate steady
increases in temperature and substantial variability with regard to future precipitation,
streamflow, evapotranspiration, and groundwater flow. Projected results for the Sprague River
basin for the decade between 2010 and 2020 under the most likely carbon emission scenarios
have been estimated, based on the overall 2000 through 2100 simulations and include:
An increase in mean maximum temperature ranging from approximately 0.36° to 0.54° F
(0.20° to 0.35° C).
An increase in mean minimum temperature ranging from approximately 0.18° to 0.81° F
(0.10° to 0.45° C).
67