Using Eddy Covariance Data for Calibrating Hydrology Models for Assessing Land Use Change Implications.

The semi-arid Southern Cotton Belt (SCB) is one of the most important cotton (Gossypium hirsutum L.) production regions in the U.S. In recent years, less water demanding crops are becoming popular in the region due to decreasing the availability of water for irrigation. The region holds enormous potential for growing cellulosic bioenergy crops, such as Alamo switchgrass (Panicum virgatum L.) and Miscanthus (Miscanthus  giganteus). Simulations of the hydrological responses and carbon dynamics of a potential land use change from cotton to cellulosic bioenergy crops provide feasibility assessment of the proposed land use on water balances and greenhouse gas emissions. The Agricultural Policy/Environmental eXtender (APEX) model was used in this study. Three-year (2013 to 2015) daily eddy covariance observations of evapotranspiration (ET) and net ecosystem exchange (NEE) and bi-weekly crop biomass data are available for four large fields in the region planted to dryland cotton, irrigated cotton, biomass sorghum and big bluestem. The APEX model was calibrated against the field observations across the spatially distributed sites and under various land uses in the Quitaque Creek watershed, which included the four fields. The calibrated APEX model will be used for evaluating the impacts of long-term land use change from cotton to perennial grasses on water and carbon dynamics. Final results from this study will be presented at this conference.