Warmer and Longer Summers Portend Increased Stream Temperatures in the Northern Rockies
A new U.S. Geological Survey study provides a larger window into the future for understanding how seasonal stream temperatures may change in one of the most ecologically diverse ecosystems in North America – the Crown of the Continent Ecosystem, USA and Canada.
Summary: Climate warming is expected to increase stream temperatures in mountainous regions of western North America, yet the degree to which future climate change may influence seasonal patterns of stream temperature is uncertain. Much of the scientific and management focus of future changes in stream temperatures has focused instead on average summer temperatures. This new study used a comprehensive database of stream temperature records (~4 million bi-hourly recordings) and high-resolution climate and land surface data to estimate monthly stream temperatures and potential change under future warming scenarios. Results imply increasing trends in stream temperature warming during spring, summer, and fall, with the largest increases predicted during summer. Additionally, stream temperatures characteristic of current August temperatures, the warmest month of the year, may be exceeded during July and September, suggesting an earlier onset and extended duration of warm summer stream temperatures. The study provides the first broad scale analysis of seasonal climate effects on stream temperature in this internationally important ecosystem for better understanding climate change impacts on freshwater habitats and guiding conservation and climate adaptation strategies for aquatic species.
The study, “Projected warming portends seasonal shifts of stream temperatures in the Crown of the Continent Ecosystem, USA and Canada”, was published in the journal Climate Change.
Salmonids – a group of coldwater adapted fishes of enormous ecological and socio-economic value – historically inhabited a variety of freshwater habitats throughout the Pacific Northwest (PNW). Over the past century, however, populations have dramatically declined due to habitat loss, overharvest, and invasive species. Consequently, many populations are listed as threatened or endangered under the U.S. Endangered Species Act. Complicating these stressors is global warming and associated climate change. Overall, aquatic ecosystems across the PNW are predicted to experience increasingly earlier snowmelt in the spring, reduced late spring and summer flows, increased winter flooding, warmer and drier summers, increased water temperatures, and expansion of invasive species. Understanding how the effects of climate change might influence habitat for native salmonid populations is critical for effective management and recovery of these species.
Future climate change is expected to dramatically alter the structure and function of freshwater ecosystems that support salmonid species. The response of salmonids to climate change will vary through space and time and manifest in both known and currently unknown ways. A potentially rich source of understanding of how salmonids interact with climate lies in a unified retrospective analysis of observed climate and population data in diverse habitats across the United States.
Climate change poses a serious threat to natural resources, biodiversity, and ecosystem services in the United States, especially in the Rocky Mountain Ecoregion. The Crown of the Continent Ecosystem (CCE) is considered one of the largest, most pristine, and biodiverse ecosystems in North America, spanning the northern Rocky Mountains of the United States and Canada. In the heart of the CCE is the Transboundary Flathead Watershed, a significant portion of which forms Waterton-Glacier International Peace Park, a World Heritage Site and Biosphere Reserve (Fig. 1). The Transboundary Flathead originates in British Columbia and flows into Montana and is considered one of America's most biodiverse river systems. Its water quality is pristine, it harbors abundant and diverse aquatic life, and it has long been recognized as a range-wide stronghold for two hallmark threatened fish species, the bull trout and the westslope cutthroat trout.