The REACH project aims to test the hypothesis that areas undergoing high rates of natural change are most vulnerable to anthropogenic or climatic change. Understanding these areas or “hotspots” is paramount in developing effective management strategies for the Minnesota River Basin.
Network Approach to River Basin Vulnerability Assessment. Landscapes are too complex to be modeled with fully distributed deterministic models that consider all the small-scale physics and interactions and require as many as a hundred calibration parameters. Besides, changes in climate, land use, and water management impose non-stationary conditions, and nonlinearities in the system make it sensitive to uncertainties and small perturbations. Recognizing these limitations, we developed a simple network-based modeling framework that focuses on understanding and predicting the emergence of “hotspots of change” and captures the most important interactions and amplifications by exploring the system connectivity and its transport pathways including residence times, threshold behavior, and physical transformations. Right: This amplification in streamflow is likely to concentrate physical, chemical, and biologic changes into “hotspots” (bottom), and the targeted management of these hotspots will most effectively improve the ecosystem.
A network approach to evaluate ecosystem vulnerability. Ecohydrologic systems exhibit shifts in behavior due to natural or human induced perturbations or stress. These shifts result from changes in dependencies between many interacting components. We use a network approach in which ecohydrologic time-series data are nodes, and information theoretic measures are links that capture various aspects of time dependencies between nodes. We construct networks from flux tower data and ecohydrologic modeling, and evaluate how they evolve in terms of connectivity, dominant time scales, link uniqueness, and link stability over time periods ranging from hours to seasons as ecosystems respond to shifting environmental conditions. Network properties can be connected with environmental conditions such as vegetation indices or species populations to detect critical interactions that may dictate ecosystem vulnerability to stress.
Demonstration of equifinality and effect on model response. The Soil and Water Assessment Tool (SWAT) is a process based model with sound scientific defensibility and numerous successful applications. However, its application requires the calibration step as with any computer model. This effort shows how multiple parameter combinations can result in similar outcomes, meaning completely different characterizations of a physical system can produce the same outcomes leading to variability in management and policy decisions. This effort highlights the importance of calibration step and efforts than can be taken to constrain equifinality. Below: Nash Sutcliffe evaluation criteria resulting from 1200 model runs of SWAT for the 2800 sq. km Le Sueur River Basin. Six different hydrologic parameters, including silt content and Peak R parameter, were varied across reasonable ranges.