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TECHNICAL REPORTS

Landscape and Watershed Processes

A Basin-Scale Approach to Estimating Stream Temperatures of Tributaries to the Lower Klamath River, California

USGS, Sacramento, CA

^* Corresponding author (lflint{at}usgs.gov).

Received for publication August 28, 2006. Stream temperature is an important component of salmonid habitat and is often above levels suitable for fish survival in the Lower Klamath River in northern California. The objective of this study was to provide boundary conditions for models that are assessing stream temperature on the main stem for the purpose of developing strategies to manage stream conditions using Total Maximum Daily Loads. For model input, hourly stream temperatures for 36 tributaries were estimated for 1 Jan. 2001 through 31 Oct. 2004. A basin-scale approach incorporating spatially distributed energy balance data was used to estimate the stream temperatures with measured air temperature and relative humidity data and simulated solar radiation, including topographic shading and corrections for cloudiness. Regression models were developed on the basis of available stream temperature data to predict temperatures for unmeasured periods of time and for unmeasured streams. The most significant factor in matching measured minimum and maximum stream temperatures was the seasonality of the estimate. Adding minimum and maximum air temperature to the regression model improved the estimate, and air temperature data over the region are available and easily distributed spatially. The addition of simulated solar radiation and vapor saturation deficit to the regression model significantly improved predictions of maximum stream temperature but was not required to predict minimum stream temperature. The average SE in estimated maximum daily stream temperature for the individual basins was 0.9 ± 0.6°C at the 95% confidence interval.

Abbreviations: D_a, day of year • DEM, digital elevation model • NCDC, National Climatic Data Center • NCRWQCB, North Coast Regional Water Quality Control Board • RAWS, Remote Automated Weather Stations • R_n, net radiation • TMDL, Total Maximum Daily Load • T_mn, minimum daily air temperature • T_mx, maximum daily air temperature • USGS, U.S. Geological Survey • VSD, vapor saturation deficit