Developing a hydro-agronomic model for assessing groundwater depletion in the Ogallala Aquifer Region

The Ogallala Aquifer Region has experienced declining groundwater levels over the past half-century due to groundwater withdrawals for irrigated agriculture exceeding mean annual recharge. To assess management strategies for groundwater use sustainability while maintaining crop yield, a hydro-agronomic model is presented that links the agricultural systems model DSSAT with the 3D groundwater flow model MODFLOW. The modeling system applies a suite of DSSAT simulations over a geographic area, with one DSSAT simulation for each cultivated field. Daily irrigation depths as specified by DSSAT are converted to pumping rates for MODFLOW, with simulated saturated thickness then used to constrain irrigation pumping rates for DSSAT during the following growing season. Python coding is used to 1) convert DSSAT output to MODFLOW pumping rates and modify input files for MODFLOW; and 2) process MODFLOW output to compute saturated thickness, update well capacity for each pumping well, and modify input files for all DSSAT simulations. The model is applied toFinney County,Kansas, which has experienced significant groundwater level declines in recent decades. The model includes 1,861 cultivated fields, consisting mostly of corn, winter wheat, sorghum, and alfalfa. Irrigation is supplied by 2,290 pumping wells. The MODFLOW model is based on a Kansas Geologic Survey MODFLOW model, with pumping rates replaced by those estimated from the DSSAT simulations. The model is tested against a large network of monitoring wells. The tested model will be used to explore the most reasonable groundwater use strategies that maintain economic prosperity and crop yield.