Station aridity in weather monitoring networks: Evidence from the Oklahoma Mesonet

Authors: SINGH, ASEEM - Oklahoma State University; TAGHVAEIAN, SALEH - Oklahoma State University; MIRCHI, ALI - Oklahoma State University; Moriasi, Daniel

Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/2023
Publication Date: 1/1/2023
Citation: Singh, A., Taghvaeian, S., Mirchi, A., Moriasi, D.N. 2023. Station aridity in weather monitoring networks: Evidence from the Oklahoma Mesonet. Applied Engineering in Agriculture. 39(2):167-177.

Interpretive Summary: Accurate estimation of water required for irrigation is critical for efficient agricultural water resources planning, management, and decision-making. The Oklahoma Mesonet provide estimates of reference evapotranspiration (ETref) to facilitate weather-informed irrigation decisions. However, weather stations that collect the required input data to estimate ETref, are not typically installed over a reference surface, defined as a large expanse of dense, well-watered, stress-free grass or alfalfa having a specified height, surface resistance, and albedo. Departure of actual surface conditions in the surrounding environment of the weather stations from the reference conditions creates weather station dryness or aridity effects that can lead to overestimation of ETref. In this study, we used daily climate datasets for a period of 20 years (2000 – 2019) to assess the prevalence and variation in space and time of weather station aridity across the Oklahoma Mesonet. Results demonstrate that weather station aridity is prevalent and highly variable in both space and time across the Oklahoma Mesonet. It increases from southeast to northwest and the Oklahoma Panhandle and highest during dry years. The weather stations with the highest station aridity are located in Texas, Cimarron, and Caddo counties, which have the largest irrigated areas among all Oklahoma counties. A better understanding of the effects of weather station aridity and application of necessary adjustments to correct overestimation in the ETref estimates can help improve the use of weather monitoring infrastructure for better agricultural water management.

Technical Abstract: Many weather monitoring networks such as the Oklahoma Mesonet provide estimates of reference evapotranspiration (ETref) to facilitate weather-informed irrigation decisions. However, weather stations that collect the required input data to estimate ETref using the widely applied Penman-Monteith method, are not typically installed over a reference surface, defined as a large expanse of dense, well-watered, stress-free grass or alfalfa having a specified height, surface resistance, and albedo. The deviation of actual surface conditions in the surrounding environment of the weather stations from the reference condition creates station aridity effects that can lead to overestimation of ETref. We use daily hydroclimate datasets for a period of 20 years (2000 – 2019) to evaluate the prevalence and spatiotemporal characteristics of station aridity across the Oklahoma Mesonet. We characterize station aridity based on mean dew point deviation (MDD = Tmin - Tdew), maximum relative humidity (RHmax), and normalized difference vegetation index (NDVI). Results demonstrate that station aridity is prevalent and highly variable in both space and time across the Oklahoma Mesonet. It increases from southeast to northwest and the Oklahoma Panhandle. Larger average seasonal MDD (up to 13 °C), lower RHmax (e.g., 57%) and NDVI (e.g., 0.22) were observed during extreme to exceptional drought of 2011 in western Oklahoma, where majority of the state’s irrigated agriculture (88%) is located. Spatiotemporal patterns of station aridity demonstrate the profound effect of wet and dry periods that influence the utility of ETref estimates to improve agricultural water conservation during high irrigation requirement times in water-scarce irrigated areas.