|Hipps, Lawrence -|
|Chavez, Jose -|
|Neale, Christopher M -|
|Agam, Nurit -|
Submitted to: Advances in Water Resources
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 10, 2012
Publication Date: November 29, 2012
Citation: Prueger, J.H., Alfieri, J.G., Hipps, L.E., Kustas, W.P., Chavez, J.L., Evett, S.R., Anderson, M.C., French, A.N., Neale, C.U., McKee, L.G., Hatfield, J.L., Howell, T.A., Agam, N. 2012. Patch scale turbulence over dryland and irrigated surfaces in a semi-arid landscape during BEAREX08. Advances in Water Resources. 50:106-199. Interpretive Summary: Semi-arid lands are characterized by hot dry conditions and are water limited. Successful agricultural production requires adequate water at precise times during crop growth. Estimating how much water is needed for proper plant development requires techniques to estimates water loss to the atmosphere through evaporation. This is often challenging in semi-arid regions because of the large areas of non-irrigated surfaces that surround irrigated surfaces which become a source of additional energy that is transported over irrigated surfaces which increase evaporation rates. A study conducted at the Conservation Production Research Laboratory (CPRL) in Bushland, TX over irrigated cotton surrounded by vast areas of parched land showed larger evaporation rates that were substantially enhanced by the transport of hot dry air surrounding the cotton site. The increases in evaporation were not accounted for by traditional evaporation model predictions. The results from this study are important to water managers and farmers who need to improve and manage limited water resources in semi-arid regions.
Technical Abstract: Quantifying turbulent fluxes of heat and water vapor over heterogeneous surfaces presents unique challenges. For example, in many arid and semi-arid regions, parcels of irrigated cropland are juxtaposed with hot, dry surfaces. Contrasting surface conditions can result in the advection of warm dry air over an irrigated crop surface where it acts to increase the water vapor deficit and, thereby, atmospheric demand. If sufficient water is present, this can significantly enhance evaporative water loss from the irrigated field. The scale and frequency of turbulent eddies over an irrigated surface during periods of strong advection is not well documented. High frequency (20 Hz) data were acquired over irrigated cotton, wheat stubble, and dry land pasture fields during the 2008 growing season as part of the Bushland Evapotranspiration and Agricultural Remote Sensing Experiment (BEAREX08). Using these data, a spectral analysis of momentum and scalar quantities including heat and water vapor was conducted revealing unique features in the turbulent structure that penetrated the surface boundary layer during periods of unusually strong advection. Wavelet analysis was also applied to assess specific events contributing to spatial and temporal structure of the turbulent flux eddies. The analysis showed that low frequency contributions were linked to both local and regional advective processes. These results clearly point to a need for better understanding of surface energy balance exchange for heterogeneous surfaces in arid and semi-arid regions under conditions of strong regional and local advection.