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Modeling Stream Temperatures with the Inclusion of Irradiance Change due to Forest Biomass Shifts.
Citation:
Halama, J., R. Mckane, Bradley Barnhart, P. Pettus, K. Djang, AND A. Brookes. Modeling Stream Temperatures with the Inclusion of Irradiance Change due to Forest Biomass Shifts. 36th Annual Salmonid Restoration Conference, Fortuna, CA, April 11 - 14, 2018.
Impact/Purpose:
This abstract is for a poster presentation at the 36th Annual Salmonid Restoration Conference 2018 conference, April 11-14, 2018, Fortuna, California, USA (https://www.calsalmon.org/conferences/36th-annual-salmonid-restoration-conference). The conference, sponsored by Salmonid Restoration Federation, will showcase professional, graduate, and undergraduate student research focusing on a: “broad range of salmonid and watershed restoration topics of concern to restoration practitioners, watershed scientists, fisheries biologists, resource agency personnel, land-use planners, and landowners” (Salmonid Restoration Federation). The conference is an excellent opportunity for EPA-WED to demonstrate how our ecological modeling and decision support tools are being designed to improve the understanding of how resource material management may impact ecosystem services. These efforts reduce model result uncertainty and usability for providing decision support for communities, tribes, and local, state and federal governments seeking to sustainably manage their respective watersheds.
Description:
Changes in stream temperature are directly and indirectly due to solar energy loading levels. Solar radiation is a significant environmental driver that impacts the quality and resilience of terrestrial and aquatic habitats, yet its spatiotemporal variations are complicated to model accurately at high resolution over large, complex watersheds. Forest disturbance regimes (e.g., fire, harvest) greatly impact the amount of solar radiation that reaches the earth’s surface. Without the explicit representation of changing shade across a dynamically growing and harvested landscape, the quantification of impacts on quality and resilience of terrestrial and aquatic habitats from land-use policies cannot be fully assessed prior to policy implementation. Here we describe the integration of a new solar energy and shade model (Penumbra) with a well-established ecohydrology model (VELMA) that simulates streamflow and plant-soil dynamics within watersheds. The Penumbra-VELMA integration is designed to simulate how forest cover and disturbance (harvest, fire, etc.) events influence ground-level solar energy over time across large spatial and temporal scales – small plots to watersheds, and minutes to centuries. Because Penumbra accounts for shading due to terrain features and vegetative object shadowing, its integration with VELMA enables important questions to be addressed concerning effects of forest management on stream flow and temperature. For example, where and how wide do riparian buffers need to be to provide adequate cold water refuges for salmonid populations during extremely hot and dry conditions? How important is the management of high elevation non-fish bearing streams for maintaining favorable temperature and flow conditions further downstream in fish-bearing streams? We developed a new stream temperature model that integrates Penumbra and VELMA simulation data to provide a new decision support tool for the assessment of watershed land-management’s potential impact on stream temperature due to solar energy shifts caused by biomass change through time. We demonstrate the impact of biomass shifts on the resulting solar energy across the Tectah Creek watershed, a sub-watershed of the Lower Klamath River Sub-basin in northern California, to produce dynamic, spatially-distributed representations of ground-level radiant flux (Kilowatts/m2/month) amidst different disturbance (i.e., harvest) regimes. These regimes included: (1) historic harvest activity replication, (2) suspended forest harvest activity, and (3) forest harvest thinning activity. Results demonstrate that this integrated modeling framework is effective at simulating dynamic high-resolution representations of ground-level energy amidst real and theoretical management scenarios over large and complex watersheds. Research presented here was aimed to demonstrate the VELMA-Penumbra integration and to reveal the potential use of the coupled models as a decision support tool for communities, tribes, and local, state and federal governments seeking to sustainably manage their respective watersheds.