Regional Efforts to Monitor and Model Stream Temperature Patterns Associated with Climate Change Across the Northwest US

Anthropogenic climate change is predicted to have profound consequences for stream ecosystems and temperature effects may be especially important given that most aquatic organisms are ectothermic. Many previous broad-scale climate assessments have relied on imprecise surrogate air temperature-elevation relationships rather than modeling stream temperatures directly due to inadequate temperature databases and modeling difficulties. The advent of inexpensive digital temperature sensors in recent decades, however, has made summer stream temperature data collection routine and large regional databases now exist (i.e., 10,000’s). These data, in conjunction with new spatial statistical models that facilitate valid interpolations between observation sites on river networks, can be used to develop regional stream temperature models that provide accurate and consistent temperature predictions for all reaches of fish-bearing streams under a variety of climate scenarios. Outputs from these models can be used to perform climate vulnerability assessments by quantifying thermal gains across entire river networks or individual streams, to describe changes in distributions of thermally suitable habitat for different fish species, and to describe spatial precision in temperature patterns. Summer stream temperature data account for the large majority of available temperature data, but also provide a narrow view of stream thermal regimes. More full-year stream temperature data are needed and are easily collected using underwater epoxies for rapid site installations and modern temperature sensors with multi-year service lives. Full-year temperature data are also less costly because < 1 site visit per year is needed rather than the current norm of two site visits for summer data. Recognition of these facts is rapidly expanding the amount of full-year temperature monitoring. Within the northwest US alone, more than 1,500 sites maintained by a dozen different resource agencies were monitoring full-year data in 2010 and another 1,000 sites were added to this monitoring network in 2011. Data from full-year monitoring sites are especially valuable for addressing a range of issues associated with how stream ecosystems may respond to climate change, including understanding the relative sensitivities of different streams to climate forcing, performing historical reconstructions to provide site-specific trend estimates, and better defining thermal criteria associated with species distributions, abundance, and developmental phenologies. In short, the ability to accurately measure and model stream temperature regimes is rapidly improving and significant advancements in our understanding of stream thermal ecology are expected in future years.