Recent Water Temperature Trends in the Lower Klamath River, California

Abstract

Elevated water temperatures have been implicated as a factor limiting the recovery of anadromous salmonids in the Klamath River basin. This article reviews evidence of a multidecade trend of increasing temperatures in the lower main‐stem Klamath River above the ocean and, based on model simulations, finds a high probability that water temperature has been increasing by approximately 0.5°C/decade (95% confidence interval (CI) = 0.42–0.60°C/decade) since the early 1960s. The season of high temperatures that are potentially stressful to salmonids has lengthened by about 1 month over the period studied, and the average length of main‐stem river with cool summer temperatures has declined by about 8.2 km/decade. Water temperature trends seem unrelated to any change in main‐stem water availability but are consistent with measured basinwide air temperature increases. Main‐stem warming may be related to the cyclic Pacific Decadal Oscillation, but if this trend continues it might jeopardize the recovery of anadromous salmonids in the Klamath River basin.

Climate change, forests, fire, water, and fish: Building resilient landscapes, streams, and managers

“…They are more a part of the internal dynamics of a complex stream/bed/aquifer system than an external driver. Historical trends in stream temperature show increases in many places in recent decades even without land cover changes (Langan and others 2001;Petersen and Kitchell 2001;Morrison and others 2002;Bartholow 2005;Hari and others 2006;Isaak and others 2010). While stream temperatures have been rising in concert with air temperatures, rates of warming are generally less than air temperature rates, and not all places are warming equally (van Vliet and others 2010).…”

Climate change, aquatic ecosystems, and fishes in the Rocky Mountain West: implications and alternatives for management

“…But for species like rainbow trout, which are constrained by temperatures that are too cold in upstream areas, warming trends may merely shift habitats toward higher elevations without causing a net gain or loss in the total amount of habitat (figure 16). Recent episodes of mortality in adult salmon linked to unusually high temperatures and low flows in the Klamath (Bartholow 2005) and Columbia rivers (Coutant 1999;Keefer and others 2007), are evidence that climate change is starting to cause acute thermal stress near downstream distribution limits and be emblematic of future changes in many populations.…”

Application of the Systems Impact Assessment Model (SIAM) to fishery resource issues in the Klamath River, California

“…The FWS, citing evidence that indicates that the hydroelectric dams cause warmer water temperatures in the fall and delayed spring warming (Bartholow, 2005), requested that the SALMOD fish production model be used to examine the effects of changing the timing of fall Chinook spawning to begin in early September instead of October. The hypothesis being tested was that cooling fall water temperatures would allow fall Chinook to immigrate and spawn earlier in the fall.…”

“…Reducing flows from 2,500 cfs to 500 cfs was shown to postpone warming to 15°C in the spring and hasten the date at which temperatures cool below 20°C in the late summer, in effect shortening the high-temperature summer season by about 7 days in the spring and 9 days in the fall (average derived from trend lines in the bottom two graphs of figure 5). Such information may be useful in light of the warming and consequent lengthening of the high temperature season that has occurred in the Klamath Basin over the last 40 years (Bartholow, 2005). Though we did not evaluate monthly flows greater than 2,500 cfs because too many of our simulations ran out of water when this flow was maintained year-round, it would not Number of exiters be difficult to do on a case by case basis as warranted.…”

“…Temperatures in the Klamath River appear to be elevated with respect to geographic regions either immediately to its north or south, in part because the river's headwater is the large, shallow Upper Klamath Lake (UKL) located in an interior basin isolated from more moderate Pacific weather (Bartholow, 2005). There are four hydropower facilities on the Klamath River below UKL all having near-surface rather than hypolimnetic withdrawal structures.…”