Classifying California's stream thermal regimes for cold-water conservation

Area of Science:

• * Stream ecology and thermal regime analysis.
• * Conservation biology and fisheries management.

Background:

• * Shift from single-metric to multi-metric thermal regime characterizations in stream management.
• * Critical need to understand cold-water persistence for declining native species, including Pacific salmon.
• * California's unique geographic and hydrological context necessitates systematic thermal regime classification.

Purpose of the Study:

• * To model and classify stream thermal regimes across California using multi-metric analysis.
• * To assess spatial variations in thermal regimes and identify influencing physical or anthropogenic factors.
• * To evaluate how classified regimes align with existing cool- and cold-water criteria and management challenges.

Main Methods:

• * Utilized long-term (> 8 years) public stream temperature data from 77 California sites.
• * Modeled thermal regimes by calculating three key temperature metrics.
• * Employed an agglomerative nesting algorithm for thermal regime classification.

Main Results:

• * Demonstrated significant spatial variation in cool- and cold-water thermal regimes across California.
• * Identified groundwater-dominated streams as a significant, understudied thermal regime class.
• * Revealed that flow regulation below dams creates artificial downstream thermal regimes.
• * Found insufficient cold-water storage in California reservoirs to replicate desirable reach-scale thermal regimes.

Conclusions:

• * Protecting resilient stream reaches is vital for cold-water species conservation amidst climate warming.
• * Existing management strategies face complications due to diverse thermal regime classifications.
• * Further research into groundwater-influenced streams and dam impacts is warranted.