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Stream isotherm shifts from climate change

Posted date: January 23, 2015
Publication Year: 
Authors: Isaak, Daniel J.;
Document type: Briefing Papers


Stream ecosystems are especially vulnerable to climate warming because most aquatic organisms are ectothermic and live in dendritic networks that are easily fragmented. Many bioclimatic models predict significant range contractions in stream biotas, but subsequent biological assessments have rarely been done to determine the accuracy of these predictions. Assessments are difficult because model predictions are either untestable or so imprecise that definitive answers may not be obtained within timespans relevant for effective conservation.

Key Findings:

  • The velocity of climate change is the rate at which isotherms shift across the landscape.
  • Calculations indicate that isotherms shift upstream at 0.13–1.3 km/decade in steep streams (2–10% slope) and 1.3–25 km/decade in flat streams (0.1–1% slope).
  • The equations predict isotherms shifted 1.5–43 km in many streams during the 20th century as air temperatures increased by 0.6°C and would shift another 5–143 km in the first half of the 21st century if projections of a 2°C air temperature increase occur.
  • Species distributions are already shifting to cooler areas (higher elevations and poleward) in response to climate change.