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.
A key challenge for resource and land managers is predicting the consequences of climate warming on streamflow and water resources. Over the last century in the western US, significant reductions in snowpack and earlier snowmelt have led to an increase in the fraction of annual streamflow during winter, and a decline in the summer. This study explores the relative roles of snowpack accumulation and melt, and landscape characteristics or 'drainage efficiency', in influencing streamflow. An analysis of streamflow during 1950-2010 for 81 watersheds across the western US indicates that summer streamflows in watersheds that drain slowly from deep groundwater and receive precipitation as snow are most sensitive to climate warming. During the spring, however, watersheds that drain rapidly and receive precipitation as snow are most sensitive to climate warming. Our results indicate that not all trends in the western US are associated with changes in snowpack dynamics; we observe declining streamflow in late fall and winter in rain-dominated watersheds as well. These empirical findings have implications for how streamflow sensitivity to warming is interpreted across broad regions.
Changes in timing and magnitudes of streamflows under climate change pose significant risks to ecosystems, infrastructure, and overall availability of water for human use. We have developed a spatial analysis that predicts how both peak (winter) and low (summer) streamflows are likely to change in the future for Oregon and Washington. This set of spatial tools gives land managers a full toolbox with which to anticipate and plan for streamflow changes on forest lands.
Bureau of Land Management, Oregon State University
FS Research Station(s):
Pacific Northwest Research Station
Natural areas are special areas set aside for research, conservation, and education. There are over 580 natural areas in Oregon and Washington totaling >1.4 million acres and managed by 20 agencies and organizations. These include Forest Service Research Natural Areas (RNAs) as well as BLM RNAs and Areas of Critical Ecological Concern. Natural areas may one of the best network of sites for studying long-term effects of climate change and this project focuses on three areas of study. The first is to determine if natural areas adequately represent the depth and breadth of the natural ecosystems found in both states. The second is to prioritize sites that may be most vulnerable to climate change effects in the next several decades. Initial findings suggest natural areas are representative across several ecological gradients important for understanding effects of long-term climate and ecological change. In addition, several lists are being developed to help prioritize monitoring based on predictions from a broad range of existing climate change models. The third area of focus is to develop a standardized set of monitoring protocols for long-term monitoring of change using existing and new protocols. New methods being tested include use of terrestrial LIDAR plots to monitor changes in forest structure over time.
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1. Prioritized list of natural areas to focus monitoring efforts. 2. Set of climate change monitoring protocols.
Massie, M. H. 2014. Assessment of the Vulnerability of Oregon and Washington’s Natural Areas to Climate Change. Master's thesis. Oregon State University, Corvallis, OR 97331.
The Forest Planner enables landowners in Oregon and Washington to find, map, and design custom forest management scenarios for their properties. Users can select the property and forest stands that they want to examine, enter information about the tree species and forest types represented, and select from a variety of management scenarios.
The Forest Planner enables landowners to visualize alternative forest management scenarios for their properties and their effect on variables including timber stocking and yields, carbon storage, and fire and pest hazard ratings.
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.