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, and while these impacts have been studied extensively at small extents, few studies have accurately modeled these impacts across watershed scales. Without the explicit representation of changing shade across a dynamically growing and harvested landscape, the quantification of land-use policies cannot be fully assessed prior to policy implementation.
Here we integrated a new solar energy model (Penumbra) with a well-established ecohydrology model (VELMA). This integration provided the ability to simulate biomass increase and loss (forest growth and harvest), and the resulting solar energy shifts for a large watershed. Penumbra, a new shade/irradiance model, simulates ground-level irradiance across large-areas. Penumbra predicts ground-level incident radiation due to terrain feature and vegetative object shadowing. VELMA (Visualizing Ecosystems for Land Management Assessment) is an ecohydrology landscape disturbance model developed to predict the effectiveness of alternative green infrastructure scenarios through the estimation of ecosystem service tradeoffs.
We integrated Penumbra and VELMA to provide a new decision support tool for the assessment of watershed land-management’s potential impact on solar energy due to biomass change over time. We demonstrate the impact of biomass shifts on the resulting solar energy across the Tolt River Watershed, a 603 square mile area East of Seattle Washington, USA, 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) intensified forest harvest activity from the years 1990 through 2010. 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 to reveal the potential use as a decision support tool for stakeholders such as: communities, tribes, and local, state and federal governments seeking to sustainably manage their respective watersheds.