Energy imbalance and evapotranspiration hysteresis under an advective environment: Evidence from lysimeter, eddy covariance, and energy balance modeling

Authors: DHUNGEL, RAMESH - Kansas State University; AIKEN, ROBERT - Kansas State University; Evett, Steven - Steve; Colaizzi, Paul; Marek, Gary; MOORHEAD, JED - Lindsay Corporation; Baumhardt, Roland - Louis; Brauer, David; KUTIKOFF, SETH - Kansas State University; LIN, XIAOMAO - Kansas State University

Submitted to: Geophysical Research Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/8/2020
Publication Date: 1/11/2021
Citation: Dhungel, R., Aiken, R., Evett, S.R., Colaizzi, P.D., Marek, G., Moorhead, J.E., Baumhardt, R.L., Brauer, D.K., Kutikoff, S., Lin, X. 2020. Energy imbalance and evapotranspiration hysteresis under an advective environment: Evidence from lysimeter, eddy covariance, and energy balance modeling. Geophysical Research Letters. 48(1). Article e2020GL091203. https://doi.org/10.1029/2020GL091203.
DOI: https://doi.org/10.1029/2020GL091203

Interpretive Summary: In water-limited regions such as the U.S. Southern High Plains, the need to conserve water resources, such as the Ogallala (High Plains) aquifer, motivates agricultural producers to know the crop water use for daily irrigation scheduling. Crop water use, also known as the evapotranspiration or ET, can be determined accurately by time consuming and expensive methods that are useable by producers in their own fields. The eddy covariance (EC) method is portable and can be set up to run automatically. However, EC method underestimates ET by 10 to 30%, with greater underestimations occurring in climates typical of the Great Plains. Therefore, ARS scientists at Bushland, Texas, cooperated with Kansas State University researchers to determine why EC systems are inaccurate with the aim to correct the errors. Scientists used direct reading weighing lysimeters to accurately measure ET and the sunlight and weather that drive ET. They then compared the lysimeter ET with computer models of ET and the EC system estimates of ET. The EC system errors could be corrected for a sorghum crop in 2014 but not for a corn crop in 2016 when conditions were drier, and hot, dry winds which caused corn water use to be large. The EC system underestimated ET by 25% overall in 2016. Although EC system design has improved over the years, ET data estimated by these systems are still less than what is directly measured. Eddy covariance systems are still not sufficiently accurate to be a guide for irrigation management or determining crop water use.

Technical Abstract: Globally, freshwater availability is threatened by climate change and modern agricultural practices. Effective use of this finite resource can be improved by better understanding of surface energy imbalance, evapotranspiration hysteresis, and advection occurrence in agricultural ecosystems. In this study, we conducted a comparison of surface energy fluxes from three distinct approaches – weighing lysimeter, eddy covariance (EC), and a two-source surface energy balance modeling (Backward-Averaged Iterative Two-Source Surface temperature and energy balance Solution: BAITSSS) for two crop seasons of 2014 sorghum and 2016 corn in Bushland, Texas. Our results suggest that ET was consistently underestimated by the EC system especially during the first half course of diurnal cycle. Energy imbalance problems in EC system were evidently associated with dynamics of hourly ET hysteresis related to both net radiation and water vapor pressure deficit. Such imbalance was resolved, on a 24-hour basis for 2014 sorghum, but not for 2016 corn. The lysimeter ET had the smallest ET hysteresis while the eddy covariance ET had the strongest hysteresis with respect to net radiation. Conversely, the lysimeter ET hysteresis was strongest compared to the eddy covariance methods when the ET was driven by the water vapor pressure deficit. The strengths of ET hysteresis related to net radiation and/or water vapor pressure deficit were obviously stronger in 2014 sorghum crops than the corn crops in 2016 regardless of advection conditions. In summary, this study provides understanding of ET hysteresis patterns, energy imbalance, and advective conditions which were associated with turbulent flux dynamics in both diurnal and crop growing seasonal scales in Bushland, Texas.