Crop Control of Evaporative Fraction in SGP

Torn, M. S., Lawrence Berkeley National Laboratory

Surface Properties

Warm Boundary Layer Processes

Bagley J, L Kueppers, D Billesbach, I Williams, S Biraud, and M Torn. 2017. "The influence of land cover on surface energy partitioning and evaporative fraction regimes in the US Southern Great Plains." Journal of Geophysical Research: Atmospheres, 122(11), 10.1002/2017JD026740.


We quantified a dramatic change in the fraction of surface energy transferred to the atmosphere as water vapor with the harvest of winter wheat, and an associated shift in control by the quantity of green leaves pre-harvest to control by soil moisture post-harvest, a shift not seen in adjacent grasslands.


The shift in relative importance of surface variables on surface energy transfer to the atmosphere demonstrates the importance of crop type and growth on the atmosphere in the Southern Great Plains, where previously scientists had thought soil moisture and net radiation were the important variables.


We synthesized and analyzed many years of land surface observations from more than a dozen Department of Energy Atmospheric Radiation Measurement observational facilities in the Southern Great Plains. We showed that during the winter wheat growing season, the quantity of green leaves and the surface-air temperature difference controlled surface energy fluxes, whereas after harvest, soil moisture was most important. For grass, leaf area was always most important.