Stream temperatures don't parallel warming climate trend

A new analysis of streams in the western United States with long-term monitoring programs has found that despite a general increase in air temperatures over the past several decades, streams are not necessarily warming at the same rate. Several factors may influence the discrepancy, researchers say, including snowmelt, interaction with groundwater, flow and discharge rates, solar radiation, wind and humidity. But even after factoring out those elements, the scientists were surprised by the cooler-than-expected maximum, mean and minimum temperatures of the streams. Results of the research, which was supported by the U.S. Geological Survey, the U.S. Forest Service and Oregon State University, have been published online in Geophysical Research Letters. "Individually, you can find streams that seem to be getting warmer and others that are getting cooler," said Ivan Arismendi, a post-doctoral researcher at Oregon State University and lead author on the study. "Some streams show little effect at all. But the bottom line is that recent trends in overall stream temperature do not parallel climate-related trends." The researchers caution that the findings don't mean that climate change will not have an impact on stream temperature, which is a fundamental driver of ecosystem processes in streams. However, the relationship between air temperatures and stream temperatures may be more complex than previously realized and require additional monitoring. Alternatively, there may be a time lag between air temperature and stream temperature, they say.