Characterizing station aridity and improving the estimates of reference evapotranspiration in the Oklahoma Mesonet

Abstract

There is a consensus among the scientific community regarding the rise in air temperatures and changing precipitation patterns across the globe. Many areas around the world are expected to see increased aridity levels in the future. The trends will likely impact the agricultural water availability, especially in water-scarce regions. As freshwater water availability declines in water-scarce agricultural regions, it is important for the producers to use it efficiently. Therefore, the objectives of this dissertation are: (1) To analyze the historical trends in temperature, rainfall, and reference evapotranspiration on a climate divisional scale across Oklahoma using the available datasets to provide insights about the implications of these trends on agricultural water management; (2) To examine station aridity in the Oklahoma Mesonet stations to investigate its prevalence and spatiotemporal patterns; and (3) To demonstrate the implications of station aridity for reference evapotranspiration and improve the estimation of the reference evapotranspiration in the Oklahoma Mesonet stations to facilitate potential irrigation water savings in the State of Oklahoma. The results reveal increasing air temperature and precipitation trends on annual and seasonal scales and decreasing reference evapotranspiration trends in summer in Oklahoma which are consistent with the findings of other researchers in the Great Plains region. Station aridity is prevalent in the dry western part of the state which hinders the Mesonet’s ability to provide accurate data on reference evapotranspiration. Station aridity effects are more pronounced during droughts, limiting the utility of the estimated reference evapotranspiration in areas and at times that accurate information is critically needed to support agricultural water conservation. It is demonstrated that air temperature and humidity datasets can be adjusted to improve the reference evapotranspiration estimates using the available and a newly developed methodology using NDVI.