Optimizing Land use Decisions Under Future Bioenergy Scenarios

The proposed increase in bioenergy usage and production will have interdependent environmental and socioeconomic impacts. Several technological pathways connect the various biomass sources to diverse forms of bioenergy (fuels, heat, and power). Currently, the complexity and scale dependency of such decisions and their impacts are not understood, defined, or described with adequate clarity to enable policy makers to develop strategies to ensure a sustainable bioenergy future with acceptable environmental and socioeconomic consequences, particularly under a changing climate regime. We have developed systems-based conceptual model of the key environmental implications of bioenergy choices and are demonstrating the utility of this approach in addressing questions of biofuel selection and deployment through the development of a spatial optimization model (SOM) that optimizes land-use decisions within a watershed. The SOM efficiently distributes where dedicated energy crops should be grown while maximizing profits (or minimizing costs) while maintaining water quality limits (nitrogen, phosphorous and sediment concentrations) and acceptable land-use displacement (e.g., area of forest, cropland, and pastured converted to energy crops). These metrics were selected from the conceptual model to represent sustainability issues and farmer choices. The SOM is parameterized using SWAT; this integration combines the decision-making power of an optimization model (i.e. SOM) with a non-linear watershed simulation tool (i.e. SWAT). This integration is a significant advance for both optimization and hydrologic/ecologic modeling allowing, for the first time, the ability to optimize spatial decisions within a watershed while maintaining water quality throughout the basin. The SOM was formulated as a mixed integer linear program (MILP), an ideal way to combine complex and competing multiple objectives with conflicting constraints. The MILP approach easily allows constraints and objectives to be interchanged, allowing the SOM to analyze watershed land-use decisions from multiple perspectives; for example, costs can be converted to a constraint (i.e., a fixed budget) and the SOM can alternatively minimize the environmental impact within the watershed while meeting a biomass target