Evaluation of Evapotranspiration from Eddy Covariance Using Large Weighing Lysimeters

Abstract

Evapotranspiration (ET) is an important component in the water budget and used extensively in water resources management such as water planning and irrigation scheduling. In semi-arid regions, irrigation is used to supplement limited and erratic growing season rainfall to meet crop water demand. Although lysimetery is considered the most accurate method for crop water use measurements, high-precision weighing lysimeters are expensive to build and operate. Alternatively, other measurement systems such as eddy covariance (EC) are being used to estimate crop water use. However, due to numerous explicit and implicit assumptions in the EC method, an energy balance closure problem is widely acknowledged. In this study, three EC systems were installed in a field containing a large weighing lysimeter at heights of 2.5, 4.5, and 8.5 m. Sensible heat flux (H) and ET from each EC system were evaluated against the lysimeter. Energy balance closure ranged from 64% to 67% for the three sensor heights. Results showed that all three EC systems underestimated H and consequently overestimated ET; however, the underestimation of H was greater in magnitude than the overestimation of ET. Analysis showed accuracy of ET was greater than energy balance closure with error rates of 20%–30% for half-hourly values. Further analysis of error rates throughout the growing season showed that energy balance closure and ET accuracy were greatest early in the season and larger error was found after plants reached their maximum height. Therefore, large errors associated with increased biomass may indicate unaccounted-for energy stored in the plant canopy as one source of error. Summing the half-hourly data to a daily time-step drastically reduced error in ET to 10%–15%, indicating that EC has potential for use in agricultural water management.

Landsat Hourly Evapotranspiration Flux Assessment using Lysimeters for the Texas High Plains

“…In addition to visual inspection of observed and simulated ET values for pixels covering lysimeters, the satellite-based ET performance was evaluated for the selected day's images that were available. Various statistical parameters were estimated, including Nash-Sutcliffe efficiency (NSE), root-mean-square error (RMSE), and mean bias error (MBE), to evaluate the relationship strength between simulated and measured values [19,43,44]. RMSE and MBE were calculated using Equations (11) and 12, respectively.…”

“…Dataloggers (CR6, Campbell Scientific, Logan, Utah) were used to collect data using the following sensors: air temperature and relative humidity sensor (HMP155, Vaisala, Helsinki, Finland), four soil water sensors (Acclima 315, Acclima Inc., Meridian, Idaho), six soil heat flux plates (HFT-3, Radiation Energy Balance Systems, Bellevue, WA, USA), an infrared thermometer, and a net radiometer (Q*7.1, Radiation Energy Balance Systems, Bellevue, WA, USA) [19]. These sensors were utilized to measure surface temperature, soil heat flux, and net solar radiation over each lysimeter.…”

Evapotranspiration and crop coefficients of Italian zucchini cultivated with recycled paper as mulch

“…Lysimetry is the most accurate method for the direct determination of evapotranspiration by soil water balance [26,27]. The operation of the drainage lysimeter is based on the principle of conservation of water mass in a soil volume.…”

Energy Imbalance and Evapotranspiration Hysteresis Under an Advective Environment: Evidence From Lysimeter, Eddy Covariance, and Energy Balance Modeling

“…Precipitation measured nearby at the surface weather station was 21 mm for 2014 and 177 mm for 2016 for the respective simulation periods. The lysimeter-measured ET (mm hr −1 ) was converted to flux (W m −2 ) using latent heat of vaporization based on ambient air temperature (T a ) as described by Moorhead et al (2019). The sensible heat flux from the lysimeter system was calculated from lysimeter LE LYS , and from R n , and G determined using methods given by Evett et al (2012a)…”