Bioenergy feedstock development scenarios & potential impacts on regional groundwater withdrawals

Availability of ample groundwater supplies for irrigation can increase the productive potential of agricultural landscapes; however, excessive withdrawals threaten sustainable use, and shortages could be exacerbated by drier future conditions in some regions. Throughout the North American Great Plains, irrigation has facilitated the conversion of grasslands to rowcrops and increased productivity, but has also decreased water table levels. Maize (Zea mays) grain is currently utilized for food and ethanol production in Great Plains agricultural landscapes, but switchgrass (Panicum virgatum) is a relatively drought tolerant, alternative biofuel feedstock that may be environmentally and economically superior to maize grain for ethanol production. Non–irrigated, small, marginally productive rowcrop fields are considered most suitable for conversion to switchgrass; however, under novel climatic conditions and ensuing agricultural policy adjustments, some larger, less productive irrigated rowcrop fields could also be converted. We developed 3 agricultural landuse change scenarios for the heavily cultivated and irrigated Rainwater Basin region of Nebraska, U.S.A., each driven by potential future climatic changes, irrigation limitations, commodity prices, and ethanol demand. For each scenario, we generated spatially explicit maps of rowcrop and switchgrass field distributions and identified registered groundwater irrigation wells. Under scenarios assuming climatic changes, annual groundwater irrigation withdrawals decreased by 3% – 6% in the entire study area, or by 10% – 19% in areas where irrigation limitations have been previously implemented and may be most severe under future conditions. In intensive agricultural landscapes where irrigation increases productivity, but may become further limited, the adoption of drought tolerant bioenergy crops could provide income for farmers while contributing to groundwater conservation efforts.