Measurements of the components of the surface energy balance (net radiation, sensible, latent and ground heat fluxes) have been measured over various ecosystems in the GCIP domain for the past several years. Observations of these fluxes indicate that on short time scales( days to weeks), the partitioning is controlled by both the water availability and the biological response of the vegetation to temperature. On longer time scales, the "green up" and "brown down" periods are also significantly modify the partitition. Examples will be shown for crop systems, forested landscapes and grasslands.