Isaak on "Downscaling Climate Change Effects on Mountain Streams and Fishes: A View from the Interior West"

Start Date/Time: Thursday, April 02, 2009, 11:00 AM
Location: Northwest Fisheries Science Center

Dr. Dan Isaak
Fisheries Biologist
Rocky Mountain Research Station

ABSTRACT

Headwater streams across the interior West are important sources of water for human uses and support critical habitats for many threatened and sensitive fishes. Rapid changes associated with a warming climate and growing human populations will exacerbate existing management challenges and pose new threats to the viability of sensitive fish populations. Many general predictions can be made regarding how climatic trends may affect stream environments, but accurate downscaling methods are needed to predict habitat changes at scales commensurate with local management activities if prioritization schemes are to proceed effectively. I will discuss two projects that are developing downscaling techniques for mountain streams, then illustrate how climate trends may already be affecting habitats for two native salmonids in a central Idaho watershed. In the first project,* *scientists at Trout Unlimited and the US Forest Service are using the Variable Infiltration Capacity (VIC) hydrologic model to derive biologically relevant flow metrics.* *These metrics will be derived for current and future thermal conditions output from a GCM and used to delineate climatically suitable niches for several native and introduced trout species across the historical range of inland cutthroat trout. In a second project, new spatial statistical models that account for network topology (i.e., flow direction and volume) are being applied with satellite imagery of riparian vegetation structure to develop a means of remotely assessing and accurately predicting summer thermal conditions across river networks. The spatial models provide valid covariance structures and improved predictive ability relative to non-spatial models---often accounting for >90% of the spatial and temporal variation in stream temperature metrics. A well-studied example that highlights how climate change may play out within an individual watershed is provided by the 6,900 km^2 Boise River basin in central Idaho. From 1993-2006, 14% of the basin burned, summer mean air temperatures increased at the rate of 0.44°C/decade, and summer flows decreased 5%/decade. These changes translated to network-averaged mean summer stream temperature increases of 0.38°C (0.27°C/decade). Within portions of the basin that burned, stream temperature increases were 2 -- 3 times greater, but the majority of basinscale temperature increases were attributable to trends in air temperature (70%) and stream flow (22%). Thermal habitats for rainbow trout were minimally affected by this warming, but bull trout habitats decreased by ~1%/year. If climate trends continue at recent rates of change, half the thermal habitat currently suitable for bull trout will disappear by the year 2056. This reduction will be exacerbated by simultaneous decreases in the number of discrete thermally suitable habitat patches, as well as the size and connectivity of these areas relative to disturbance processes. Moreover, estimates of bull trout habitat losses may prove conservative because the distribution of future fires and subsequent post-fire disturbances is unknown, and because climatic extremes and their persistence are increasing more rapidly than mean trends. More work is needed to provide biological validation of predicted habitat trends, understand habitat geometries that confer population resilience, map fire threats, and provide decision support. As these needs are met, it will be possible to do the high resolution, species-specific risk assessments throughout river networks that are necessary to inform proactive management and intelligently adapt to a warming climate.

BIO

*_Information on Dan Isaak's bio and research is available at http://www.fs.fed.us/rm/boise/AWAE/scientists/profiles/AWAIsaak.shtml

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