Biological Opinions - Bureau of Reclamation

7.9.2 Klamath Basin
The Oregon Climate Division 5 (includes the high plateau area of the upper Klamath Basin)
temperature dataset and the U.S. Historical Climatology Network temperature dataset for Crater
Lake show warming trends in winter temperatures since the 1970s (Mayer 2008). 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 (2011) reports that the
mean annual temperature in Jackson and Klamath Counties, Oregon, and Siskiyou County,
California, increased by slightly less than 1.8º F (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 2011).
In conjunction with rising temperatures, snow water equivalent has been declining. Regonda and
others (2005) analyzed western states data from 1950 through 1999, including data from the
Cascade Mountains of southern Oregon. Their findings show a decline in snow-water equivalent
of greater than 6 inches (15.24 cm), an approximate 20 percent reduction in snow water
equivalent, during March, April, and May in the southern Oregon Cascades for the 50-year
period evaluated.
Analysis of climatologic and hydrologic information for the upper Klamath Basin indicates UKL
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 UKL
from 1981 through 2012, and also demonstrate declining flows in the Sprague and Williamson
Rivers (major tributaries to UKL) during the POR. However, trends change markedly depending
on the selected period of record and trends for different time frames (e.g. 1991 through 2012 and
2001 through 2012) demonstrate increasing net inflow to UKL. Inflow to UKL and flow in the
Sprague and Williamson Rivers are strongly dependent on climate, particularly precipitation, as
demonstrated in 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, and
increasing surface water diversions or groundwater pumping upstream of UKL (Mayer 2008;
Mayer and Naman 2011).
Projections of the effects of climate change in the Klamath Basin suggest temperature will
increase in comparison to a 1961 through 2000 comparison period (Barr et al. 2010; U.S. Bureau
of Reclamation 2011). 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 2011). During the
2035 and 2045 period, temperature increases are expected to range from 2.0 to 3.6° F (1.1 to 2.0°
C), with greater increases in the summer months and lesser increases in winter (Barr et al. 2010).
Effects of climate change on precipitation are substantially more difficult to estimate and models
used for the Klamath Basin suggest decreases and increases. During the 2020s, Reclamation
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