LESSONS LEARNED FROM THE BUSHLAND EVAPOTRANSPIRATION AND AGRICULTURAL REMOTE SENSING EXPERIMENT 2008 (BEAREX08)

In 2008, a team of USDA and university researchers assembled to study the surface energy balance and associated energy and water fluxes within, below and above the internal boundary layers over irrigated and dryland cotton crops in the hot, windy and advective environment of the Texas Panhandle at Bushland. This Bushland Evapotranspiration and Agricultural Remote sensing EXperiment 2008 (BEAREX08) was designed as a multi-instrument study of energy and water balances focused on determining evapotranspiration (ET) at multiple scales. Subsurface measurements of soil water storage accomplished using both weighing lysimeters and networks of deep neutron probe readings were used with measurements of irrigation applications and precipitation to determine the ET based on mass balance, which was then compared with ET estimates derived from eddy covariance (EC) and surface energy balance models. Gaps in knowledge and limitations of all methods were evidenced and accentuated due to the severely advective conditions and the spatial variability of ET, which was related to plant cover and water balance variations in space. The EC methods were shown to consistently under estimate ET in this environment, which likely routinely violated assumptions of equilibrium conditions. During the 2008 season, ET measured using weighing lysimeters was shown to be representative of ET in the surrounding field when plant cover on a lysimeter was similar to that in the field, and to not be routinely representative of the surrounding fields when plant stature and cover factor deviated from that in the surrounding field. Larger scale determinations of energy and water fluxes were based on flux aircraft and aerial and satellite remote sensing. We will share lessons learned and avenues of inquiry elucidated by this multi-institutional study. Chief among these was the importance of vadose zone water balance and flux determinations to improving accuracy of earth surface water flux estimates.