The difficulties posed by an arid and heterogenous landscape in quantifying the surface energy balance are considered. Eddy covariance (EC) and Bowen Ratio (BR) techniques were used to estimate sensible and latent heat fluxes over two plant communities in the Jornada Rangeland near Las Cruces, NM. These included a grass-dominated community, and a very heterogeneous honey mesquite plant community. The BR produced reasonable results over the grass site, though there was a bias present. Over the mesquite site the BR results were inconsistent under wet conditions, and failed completely under dry conditions. Several issues which relate to the problems of the BR approach are examined, including resolution of small gradients of humidity and spatial variations in available energy. One issue in arid landscapes is that available energy may not be estimated at the same scale as that of the turbulent flux measurements. To address this, the footprints of the fluxes were estimated using the published models by Schuepp et al. (1990) and Schmid (1994). The spatial variations in available energy were estimated from high resolution remote sensing data, which allowed the 2 dimensional distribution of vegetation and soil to be quantified. The spatial properties of these data will be identical to those of available energy. These results will allow us to aggregate up available energy estimates from the point measurements to larger regions. These findings will suggest the spatial scales at which available energy must be estimated to be commensurate with the footprints of the flux measurements. The results indicate the key problems and the related issues in determining the energy balance in arid regions. In addition, they suggest the utility of remote sensing data in estimating the spatial variations in surface properties related to energy balance.