Citation:

Detenbeck, N., M. Fuller, P. Leinenbach, D. Brown, D. Isaak, AND S. Figary. Incorporating climate into management strategies for protection of thermal regimes: Three case studies. Thermal Complexity Workshop Part II: Climate, NA, WA, May 01, 2023.

Impact/Purpose:

Management of stream thermal regimes for protection of coldwater fish species such as salmonids requires knowledge of how the distribution of coldwater habitat changes over space and time.  Thermal regimes are not just changing seasonally, but also over decades in response to climate change with shifts in air temperature, precipitation patterns, and shade as forest fires increase.  Spatial stream network (SSN) models provide one mechanism for evaluating complex thermal regime patterns over space and time.  We discuss three case studies to demonstrate how SSN models can be used to explore distribution of cold water habitat and coldwater refuge areas along migration corridors.  Finally, advances in technology are allowing us to efficiently create fine-resolution models over broad regions capable of predicting effects of forested buffer width and extent on shade and stream thermal regimes.

Description:

Spatial stream network (SSN) models for stream/river temperature are being applied in conjunction with climate change model projections to project effects of riparian vegetation management on protection of thermal regimes and cold water refuge areas.  Using a regional medium-resolution SSN temperature model with covariates representing shade effects we predicted mean August stream temperatures across 78,195 km of tributaries flowing into the Columbia River in the northwestern United States. We evaluated nine scenarios predicting stream temperatures for three riparian shade conditions (current, restored, and no riparian vegetation) within three  different climate periods (2000s, 2040s, and 2080s).  Results suggest riparian shade restoration (2000s climate) could decrease mean August stream temperatures by 0.62¿C across the study network and reduce temperature of tributaries at their confluence with the Columbia River (potential refuge areas) by 0.02 to 2.08¿C compared with current shade conditions. The climate warming effect predicted for the 2040s and 2080s, however, is greater than the cooling effect from restoring riparian shade.  In Oregon, the proportion of fish habitat for salmon and trout rearing and migration that meet temperature numeric water quality criteria could be increased by 20% by restoring shade conditions, although net habitat declines may still occur in the future.  In the transboundary Meduxnekeag (New Brunswick/Maine) watershed, we worked with the Maliseet tribe to develop and apply a fine-resolution SSN model based on the high resolution NHDPlus framework to evaluate performance of different width riparian buffers on protection of cold- and coolwater thermal regimes under varying weather regimes. Riparian buffer effects on stream temperatures extended downstream by 3 h travel time or 1 km network distance.  Monthly models predicted the fewest cold water (<19.0 °C) reaches in July with 28% in the dry and 68% in the wet year. Growing season maximum (GSM) predictions found 81% of stream reaches could not support salmonid survival (>27.0 °C) in the dry year and 59% of the reaches were warmwater (22.5–27.0 °C) in the wet year. Restoration scenarios (30 or 90 meter forested buffers) expanded cold water habitat based on monthly median temperatures and decreased the habitat area with GSM above survival thresholds, with little difference in effectiveness of the two buffer widths.  In the Upper Rogue River watershed in Oregon, we are applying a hybrid SWAT-fine resolution SSN model to evaluate the effectiveness of different riparian buffer management practices under both recent historic and future climate regimes.  For current and future climate scenarios, we are comparing effectiveness of current vegetation conditions, an antidegradation scenario (110 foot buffers on both fish-bearing and fishless streams), and a forest management scenario consistent with proposed Oregon Forest Plan guidance (100 to 110 foot buffers on fish-bearing streams, 75 foot buffers on contiguous upstream reaches, and a 35 foot streamside zone with only equipment limitations on fish-less streams).  Recently we have developed R programs with parallel processing to generate inputs to shade models and to implement Chen’s shade algorithms in the cloud to enable us to efficiently generate fine resolution SSN models across broad spatial scales, allowing these approaches to be regionalized.

Record Details: