The Interplay of Bioenergy Crop Production and Water Resource Availability in the US

Large-scale growing of bioenergy crops, such as switchgrass (Panicum viragatum) and Miscanthus (Miscanthus x giganteus), may introduce new challenges for water resource availability in the US. However, the strength of the interplay between bioenergy crop production and water resource availability is highly uncertain at the spatial scale and determined by (1) the spatial distribution of land cover types; (2) availability of soil water resources; (3) climate conditions and (4) biophysical characteristics of different bioenergy crops, such as water use efficiency (WUE), tolerances to extreme water and thermal conditions (dry, high temperature, low temperature etc.) and photoperiod adaptability, etc. To address potential water availability concerns the spatial distribution of bioenergy crops needs to be optimized by considering the maximum WUE and the minimum dependence and impact on water resource availability. To address this objective, we apply a coupled biophysical and biogeochemical model (ISAM), to investigate spatial variability in the interplay between water resources and bioenergy crop production in the US. The bioenergy crops considered in this study include Miscanthus, Cave-in-Rock and Alamo switchgrasses, and corn (grain and stover). The interplay between bioenergy crop and corn production with water resources is quantitatively evaluated by calculating WUE and average water stress for different bioenergy crops and change in plant available soil water between bioenergy crops and natural vegetation. Our results indicate that low soil water availability limits production of bioenergy grasses in central and eastern Great Plains. Growing energy grasses here strengthens water depletion and limits its potential production. Miscanthus has the highest WUE in the central Midwest, followed by corn stover and Cave-in-Rock. However, growing Miscanthus and Cave-in-Rock here strengthens soil water depletion and induces water stress on their production. Though production of Miscanthus and Alamo in the upper Midwest and Cave-in-Rock and Miscanthus in the southern US do not depend on and impact water resource availability, their WUE is low here. Corn and Cave-in-Rock has higher WUE than other grasses in the upper Midwest, whereas Alamo has the highest WUE of all bioenergy grasses in the southern US.