NWC REU 2019
May 21 - July 30



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The Atmospheric Demand For Moisture in the Great Plains

Raquel Dominguez, Ryann Wakefield, Jordan Christian, and Jeff Basara


What is already known:

  • In previous research models have shown that there has been an eastward movement of the aridity gradient in the Great Plains.
  • The increase of potential evapotranspiration causes aridity to increase more in the east than in the west, indicating that the eastern Great Plains are prone to experience a drier climate.
  • Finding a dominant driver of aridity, either potential evapotranspiration or precipitation, is also studied on annual and monthly timescales.
  • Understanding complex aridity behavior within a climatological record will aid in bringing awareness for agricultural practices and drought management on the Great Plains.
  • Whether the aridity gradient in the Great Plains is shifting using an reanalysis dataset is unknown.

What this study adds:

  • Verification of the North American Regional Reanalysis accuracy by comparing to variable computations from the Oklahoma Mesonet.
  • Contrary to previous findings, results show that using observational and modeled data the aridity gradient is diffusing over the Great Plains.
  • Based on annual trend analysis, potential evapotranspiration and precipitation share an equal role in the dominance within aridity.
  • Despite high variation of all variables throughout space and time, precipitation shows dominance over aridity index within a monthly climatological record.


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.

Full Paper [PDF]