Modeling the effects of land use change from cotton (Gossypium hirsutum L.) to perennial bioenergy grasses on watershed hydrology and water quality under changing climate

Assessing the impacts of biofuel-induced land use change on hydrology, water quality and crop yield under the current and future climate scenarios enables selection of appropriate land uses and associated best management practices under the changing climate. In this study, the impacts of land use change from cotton (Gossypium hirsutum L.) to perennial grasses in the Double Mountain Fork Brazos watershed in the Texas High Plains were assessed using the Soil and Water Assessment Tool (SWAT). While switchgrass (Panicum virgatum L.) was assumed to replace cotton in irrigated areas, dryland cotton was replaced by Miscanthus×giganteus under the hypothetical land use change scenarios. Climate change impacts were assessed based on the Coupled Model Intercomparison Project Phase 5 (CMIP5) climate projections of 19 General Circulation Models (GCMs) under two Representative Concentration Pathway (RCP) emission scenarios of RCP4.5 and RCP8.5 during two 30-year periods of middle (2040–2069) and end (2070–2099) of the 21st century. Median irrigation water use of cotton was simulated to decrease by 41%–61% in the future when compared to historic (1994–2009) period based on projections by 19 GCMs. Under the future climate change scenarios, when compared to cotton, median annual irrigation water use by switchgrass reduced by 62%–89%. Simulated future median total nitrogen load decreased by 30%–40% under perennial grasses when compared to future cotton land use. The median irrigated switchgrass yield decreased by 16%–28%, but the median dryland Miscanthus yield increased by 32%–38% under the future climate change scenarios.