101528 Differences in Evapotranspiration from Eddy Covariance and Lysimeters in Advective Conditions.

Poster Number 322-523

See more from this Division: ASA Section: Climatology and Modeling
See more from this Session: Evapotranspiration Measurements and Modeling Poster (includes student competition)

Tuesday, November 8, 2016
Phoenix Convention Center North, Exhibit Hall CDE

Seth Kutikoff1, Xiaomao Lin2, Steven R. Evett3, David K. Brauer3, Prasanna H. Gowda4, Jerry Edgar Moorhead3, Robert M. Aiken5, Paul D. Colaizzi3 and Gary Marek3, (1)Kansas State University, Manhattan, KS
(2)Kansas State University, Kansas State University, Manhattan, KS
(3)USDA-ARS Conservation and Production Research Laboratory, Bushland, TX
(4)USDA-ARS Grazinglands Research Laboratory, El Reno, OK
(5)105 Experiment Farm Road, Kansas State University, Colby, KS
Poster Presentation
  • ASAPoster2016Kutikoff.pdf (1.0 MB)
  • Abstract:
    Direct measurements of evapotranspiration (ET) in irrigated agriculture are often made through either a soil water balance with lysimeters or energy balance with eddy covariance (EC). Both systems operate at a high measurement frequency that must be averaged over a more stable period, with the lysimeter affected by wind loading and EC system unable to resolve large eddies associated with sensible heat advection. In this experiment, we compared rates of ET at a typical flux averaging period of thirty minutes with that of a shorter averaging period of five minutes. During the 2015 sorghum growing season in Bushland, TX, three EC systems at 2, 4, and 8 meters above ground were evaluated against a large weighing lysimeter located a short distance upwind of the EC tower. ET was processed and compared for 19 non-consecutive days amidst a thirty-two day period when the crop was well-developed. Advective conditions were identified based on wind direction and the ratio of available energy to latent heat. We found that wind speed was important for measurement error above a threshold of around 2 m s-2 in the well mixed air above the canopy, but error magnitude is mostly very small relative to lysimeter calibration. Daytime fluxes were higher with longer averaging time, with the lowest EC system generally more accurate on both five and thirty minute timescales. Our results are mostly consistent with previous ET studies in this semi-arid location indicating systematic underestimation of ET by EC systems on a daily timescale relative to the lysimeter.

    See more from this Division: ASA Section: Climatology and Modeling
    See more from this Session: Evapotranspiration Measurements and Modeling Poster (includes student competition)