Modified equilibrium temperature models for cold-water streams

Water temperature determines the spatial distribution of fish species, including cold-water fish such as trout, and is driven by the balance of the heat flux across the water surface and the heat flux across the sediment surface. In this study, a modified equilibrium temperature model was developed for cold-water streams that includes the effect of groundwater inflow. The modified equilibrium temperature model gives estimates of daily average stream temperature based on climate conditions, riparian shading, stream width, and groundwater input rate and temperature. For a small tributary stream with relatively uniform riparian shading, the modified equilibrium temperature was found to be a good predictor of daily average stream temperature, with a root-mean-square errors (RMSE) of 1.2C. The modified equilibrium temperature model also gave good estimates (1.4C RMSE) of daily average stream temperature for a larger stream when riparian shading was averaged over sufficiently long distances. A sensitivity analysis using the modified equilibrium temperature model confirmed that water temperature in cold-water streams varies strongly with riparian shading, stream width, and both groundwater inflow rate and temperature. These groundwater parameters therefore need to be taken into account when climate change impacts on stream temperature are projected. The stream temperature model developed in this study is a useful tool to characterize temperature conditions in cold-water streams with different levels of riparian shading and groundwater inputs and to assess the impact of future land use and climate change on temperature in these streams.