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Title: On the long-term hydroclimatic sustainability of perennial bioenergy crop expansion over the United States

item WANG, M - Arizona State University
item WAGNER, M - Arizona State University
item MIGUEZ-MACHO, G - Universidad De Santiago De Compostela
item KAMARIANAKIS, Y - Arizona State University
item MAHALOV, A - Arizona State University
item MOUSTAOUI, M - Arizona State University
item MILLER, J - University Of Illinois
item VANLOOCKE, A - Iowa State University
item BAGLEY, J - Lawrence Berkeley National Laboratory
item Bernacchi, Carl
item GEORGESCU, M - Arizona State University

Submitted to: Journal of Climate
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/6/2016
Publication Date: 4/1/2017
Citation: Wang, M., Wagner, M., Miguez-Macho, G., Kamarianakis, Y., Mahalov, A., Moustaoui, M., Miller, J., VanLoocke, A., Bagley, J.E., Bernacchi, C.J., Georgescu, M. 2017. On the long-term hydroclimatic sustainability of perennial bioenergy crop expansion over the United States. Journal of Climate. 30:2535-2557.

Interpretive Summary: Biofuels can reduce the release of carbon dioxide, a potent pollutant, in to the atmosphere compared with using fossil fuels such as coal and oil. Biofuel species can also drive a reduction in surface temperatures due to the plant using more water. However, the impact might this have on soil moisture could potentially offset many of the benefits. Here we used models that are built on measurements of perennial grasses ideally suited to be bioenergy crops to assess the potential offset between land use changes impacts on greenhouse gas warming, net cooling from increased water use, and losses of soil moisture. Here was how that cooling occurs when existing land used are transitioned to bioenergy crops. However, the impacts of soil drying vary across the study region. These results help to reveal strategies to implement bioenergy crops in regions well suited for the impacts that they have and to avoid planting in areas where the consequences can offset the potential benefits.

Technical Abstract: Large-scale cultivation of perennial bioenergy crops (e.g., miscanthus and switchgrass) offers unique opportunities to mitigate climate change through avoided fossil fuel use and associated greenhouse gas reduction. Although conversion of existing agriculturally intensive lands (e.g., maize and soy) to perennial bioenergy cropping systems has been shown to reduce near-surface temperatures, unintended consequences on natural water resources via depletion of soil moisture may offset these benefits. The hydroclimatic impacts associated with perennial bioenergy crop expansion over the contiguous United States are quantified using the Weather Research and Forecasting model dynamically coupled to a land surface model (LSM). A suite of continuous (2000–09) medium-range resolution (20-km grid spacing) ensemble-based simulations is conducted using seasonally evolving biophysical representation of perennial bioenergy cropping systems within the LSM based on observational data. Deployment is carried out only over suitable abandoned and degraded farmlands to avoid competition with existing food cropping systems. Results show that near-surface cooling (locally, up to 5°C) is greatest during the growing season over portions of the central United States. For some regions, principal impacts are restricted to a reduction in near-surface temperature (e.g., eastern portions of the United States) whereas for other regions deployment leads to soil moisture reduction in excess of 0.15–0.2 m3m-2 during the simulated 10-yr period (e.g., western Great Plains). This reduction (25%–30% of available soil moisture) manifests as a progressively decreasing trend over time. The large-scale focus of this research demonstrates the long-term hydroclimatic sustainability of large-scale deployment of perennial bioenergy crops across the continental United States, revealing potential hot spots of suitable deployment and regions to avoid.