What is already known:
What this study adds:
Changes in the demand for moisture by the atmosphere can significantly impact the vulnerability of ecosystems to drought. Between arid and humid regions lies a transition zone where a significant gradient in aridity also exists. This aridity gradient can shift depending upon changes in precipitation and atmospheric demand. Thus, we employ a metric known as the aridity index which is defined as the ratio of precipitation to potential evapotranspiration (PET), where PET represents the atmospheric demand for moisture. The aridity index allows for identification of climatological patterns in atmospheric demand and any deviations from those patterns. The individual components of aridity, which are precipitation and PET, were also analyzed to better understand which variable contributed to changes in aridity. Using reanalysis and observational data, this study focused on the Great Plains of the United States, which is a climatological transition between arid and humid climates. We found the gradient becomes weaker with time across the Great Plains. The trends found using North American Regional Reanalysis data were compared to observations by calculating aridity using Oklahoma Mesonet data, and these trends could have significant implications for agricultural practices and drought management on the Great Plains.