Energy and Water Fluxes across a Heterogeneous Landscape in the Southern Great Plains

Abstract:

Fluxes of energy and water between the atmosphere and the land surface influence weather and climate. These fluxes depend on the state of the landscape, which contributes to differences in land-atmosphere coupling strength over space and time. One region with potentially strong land-atmosphere coupling is the Southern Great Plains (SGP) in North America. In this region, managed vegetation plays a key role in moderating the surface energy through effects on surface albedo, transpiration, precipitation interception, and other surface properties. However accurately modeling these effects is challenging because the vegetation in this region is very heterogeneous. Winter wheat is the dominant crop, but pasture, hayfields, corn, and recently introduced crops such as canola cover significant portions of the landscape as well. Winter wheat has a unique phenology with fall planting, maximum leaf area in late spring, and harvest in early summer. This phenology contrasts significantly with most other crops and with pastures and hayfields in the region, which have more typical spring-fall growing seasons. Therefore, to sufficiently model and assess land–atmosphere interactions in this region accurate characterization of differences in the seasonality of water and energy fluxes between vegetation types are necessary. We used observations including eddy covariance flux estimates, soil moisture data, state-of-the-art longwave and shortwave radiation measurements, and other observations available for several facilities within the SGP Atmospheric Radiation Measurement (ARM) site in north-central Oklahoma and southern Kansas. We compared the timing and variations in fluxes of water and energy between winter wheat and other land cover types, focusing on vegetation influences on rates of soil dry-down following precipitation events. We found distinct differences in fluxes between winter wheat and other land types. These flux differences had a nonlinear dependency on disparities in leaf area index, and were particularly pronounced in the period following the summertime wheat harvest when differences in latent heat flux greater than 50 Wm^-2 were commonly observed.