Seasonal water-level perturbations beneath the high plains of the Llano Estacado

•A method for computing water-level perturbation curves was developed.•Water-level perturbations are defined as deviations from a nonstationary mean water level.•Perturbation curves follow seasonal patterns of high water levels in winter and low levels during the growing season.•This technique provides insight into how the collective actions of farmers affect the Ogallala Aquifer.