Mega-Drought Effects on Evapotranspiration and Energy Balance of a Pasture in the Southern Great High Plains.

Understanding the energy exchange processes between changing land cover types and atmosphere is important in studying the feedbacks between vegetation and climate.  Changes in surface properties due to land cover changes significantly affect water vapor and heat exchange between biosphere and the atmosphere through changes in albedo, surface roughness, leaf area, and biomass. Ecosystem-level fluxes can be quantified with fast-response instruments using the eddy covariance method.  It has been widely used around the world for studying the energy exchange processes and hydrological cycles of different ecosystems. In the near-future, managed grasslands and pastures could emerge as a dominant land cover type in the Southern Great Plains region due to increasing variability in climate, ground water depletion, and pumping restrictions.  The exceptional drought in 2011 offers a special chance to investigate the impact of an extreme drought event on water vapor and heat fluxes from a managed WW B-Dahl pasture in the Southern Great Plains.  The objectives of this study were to assess the impact of the mega-drought event of 2011 on energy and water vapor fluxes from this pasture during the peak growing season (June-August) and compare the results to the preceding year which was a year with above-normal rainfall.  We also examined the effects of seasonal changes in net ecosystem production (NEP), weather, and soil moisture content on energy fluxes and canopy conductance characteristics.