What will the rivers of the Pacific Northwest look like in the future? Will they be stable or unstable? Will they have salmon or other species? Will the waters be cold and clear or warm and muddy? These questions motivate our study of the effects of climate warming on streams draining the Cascade Mountains.
Previous studies have shown that snowpacks throughout the Cascades are highly vulnerable to warming temperatures, readily changing from snow to rain, and melting earlier. Less certain is how these changes are likely to affect streamflows, particularly in streams that derive much of their flow from deep groundwater and springs. These groundwater streams, which are currently characterized by very stable bed, banks, and vegetation, are particularly sensitive to increasing peak flows in the winter. We want to know how changing snowpacks and increased peak flows are likely to affect these channels, potentially changing their suitability as habitat for threatened species such as bull trout and spring Chinook. Results from our work, which include field and modeling components, will be used to guide management decisions affecting these streams: how dams are operated, whether water suppliers need to worry about turbidity, and how we should manage riparian vegetation.
Restoring riparian forests on streams where historic land uses have created open meadows could reduce maximum stream temperatures by as much as 7o C relative to current conditions, even under a future climate when air temperatures are 4o C warmer than today.
Summer maximum stream temperatures are near thresholds of thermal tolerance for salmon and trout in many streams throughout the interior Columbia River Basin. Salmon and trout populations in many of these streams are severely depressed, resulting in efforts to restore stream and riparian habitat. Climate change raises serious questions about the long-term outcomes of restoration because projected warming could make many of these streams and rivers uninhabitable for salmon and trout within a few decades.
We used the mechanistic stream temperature model, HeatSource, to examine future changes in stream temperature on the upper Middle Fork John Day River. Our model scenarios examined: 1) a +4 oC increase in air temperature; 2) ±30% changes in stream discharge from both changes in irrigation withdrawals and climate-change related loss of winter snowpacks; and 3) four riparian vegetation scenarios: 3a) current conditions where effective stream shade averages 19%; 3b) a post-wild fire scenario with maximum vegetation height of 1 m and 10% canopy density resulting in 7% effective stream shade; 3c) an intermediate condition representing a young-open forest or tall-shrub dominated vegetation with trees or shrubs 10-m tall and with 30% canopy density resulting in 34% effective shade; and 3d) a restored riparian forest with trees 30-m high and canopy density of 50% resulting in 79% effective stream shade.
Our model results showed the composition and structure of riparian vegetation were the single biggest factor determining future stream temperatures. In contrast, changing air temperature or stream discharge had relatively small influence on future stream temperatures. The post-wildfire and the current-vegetation scenarios were warmer than today, but in both cases, effective shade was low, so the stream was sensitive to air temperature increases due to climate change. The intermediate restoration, simulating a young-open forest or a tall-shrub dominated riparian zone, was slightly cooler than today. The biggest change resulted from restoring the riparian forest which decreased summer maximum temperatures by ~ 7 oC.
Stream data are needed to enable managers to understand baseline conditions, historic trends, and potential impacts of climate change on stream temperature and flow, and in turn on aquatic species in freshwater ecosystems.
NorEaST is being developed to provide a coordinated, multi-agency regional web portal to compile, store, map, and distribute continuous stream temperature locations and data across the Northeastern U.S.
Provides an example of how to bring the flood of data and information on climate change together to prioritize conservation and management, using an example of a model for Bull trout in the Boise River basin.
Many new tools are becoming available to provide downscaled climate data and help us make management decisions. How do these tools perform when used in an excersize to examine real-world problems? See the example of an exercise done for Bull Trout.