Preliminary Findings
Preliminary Findings
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After calculating the highest weekly average daily maximum temperature (or Max 7DADM, a common metric used for assessing stream temperatures) for 80 sites during the summers of 2021, our team was able use these values to build a SSN model for 2021.
While stream temperatures generally decrease with elevation and decrease with air temperature, other potential explanatory variables emerged which help explain sub-watershed variation in the data. These include severe impacts from the 2020 Riverside Fire, as well as the influence of the Upper Clackamas's relatively young high cascades geology and numerous cold groundwater inputs.
When compared to a traditional non-spatial linear model, our SSN performed with a much higher degree of certainty and more variation in the stream temperature data explained.
Model results for 2021 stream temperature:
Above figure: 2021 continuous predicted stream temperatures with standard errors. The size of the gray line below each prediction indicates the prediction standard errors; thicker lines have higher prediction standard errors, thus less confidence in a point it stands out more in the graphic. Standard errors range from 0.4 to 2.7.
Above table: Summary of spatial stream network (SSN) and multiple linear regression (MLR) models that explain stream temperature. Parameter estimates represent the regression coefficient, which equals change in the stream temperature based on a 1-unit change in the predictor variable with all other variables being constant. Variance components assign variance in stream temperature to explanatory variables, flow-connected stream distance, and unexplained variance.
Location of the image on the right, showing the different colors of the two Clackamas River tributaries resulting in varying underlying geologic types.
The effect of differences in underlying geology on these tributaries' turbidity is apparent during periods of high flows, where the older, deeply eroded western cascades geology of the Collawash River meets the younger high cascades geology of the Upper Clackamas.
During the summer of 2023, 2e collected stream temperature data at over 100 sites, marking the largest monitoring effort in the basin's history!
Our 2024 activities will include gathering all available stream temperature data, starting in 1991 in order to build a SSN model for the historic time period which will lead to the development of a model predicting 2050 and 2080 stream temperatures under climate change scenarios. This, combined with current salmonid distribution information on the basin, will allow realistic intrinsic salmonid habitat maps to be produced for these future time periods.
Left: distribution of stream temperature data collected from 1991 to 2023, symbolized by the sub-watershed from which it was collected.
Below: spatial distribution of stream temperature data collected on the basin across time.
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