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AGU: Geophysical Research Letters

 

Keywords

  • aquatic ecology
  • climate change
  • disturbance
  • freshwater ecosytems
  • hydrology
  • reference sites

Index Terms

  • 0496 - Water quality
  • 1616 - Climate variability
  • 1630 - Impacts of global change
  • 1807 - Climate impacts
  • 9350 - North America

Paper in Press

GEOPHYSICAL RESEARCH LETTERS, doi:10.1029/2012GL051448

The paradox of cooling streams in a warming world: Regional climate trends do not parallel variable local trends in stream temperature in the Pacific continental United States

Key Points
  • Recent trends in stream temperature do not parallel climate-related trends
  • Minimally human-influenced streams are not showing consistent warming trends
  • Greater complexity than previously assumed in thermal regimes of streams

Authors:

Ivan Arismendi

Sherri Johnson

Jason Dunham

Roy Haggerty

David Hockman-Wert

Temperature is a fundamentally important driver of ecosystem processes in streams. Recent warming of terrestrial climates around the globe has motivated concern about consequent increases in stream temperature. More specifically, observed trends of increasing air temperature and declining stream flow are widely believed to result in corresponding increases in stream temperature. Here, we examined the evidence for this using long-term stream temperature data from minimally and highly human-impacted sites located across the Pacific continental United States. Based on hypothesized climate impacts, we predicted that we should find warming trends in the maximum, mean and minimum temperatures, as well as increasing variability over time. These predictions were not fully realized. Warming trends were most prevalent in a small subset of locations with longer time series beginning in the 1950s. More recent series of observations (1987-2009) exhibited fewer warming trends and more cooling trends in both minimally and highly human-influenced systems. Trends in variability were much less evident, regardless of the length of time series. Based on these findings, we conclude that our perspective of climate impacts on stream temperatures is clouded considerably by a lack of long-term data on minimally impacted streams, and biased spatio-temporal representation of existing time series. Overall our results highlight the need to develop more mechanistic, process-based understanding of linkages between climate change, other human impacts and stream temperature, and to deploy sensor networks that will provide better information on trends in stream temperatures in the future.

Received 20 February 2012; accepted 12 April 2012.

Citation: Arismendi, I., S. Johnson, J. Dunham, R. Haggerty, and D. Hockman-Wert (2012), The paradox of cooling streams in a warming world: Regional climate trends do not parallel variable local trends in stream temperature in the Pacific continental United States, Geophys. Res. Lett., doi:10.1029/2012GL051448, in press.