The Earth’s surface contains small heterogeneities in land cover; however, atmospheric models treat the land surface is homogenous over kilometers. Understanding how surface heterogeneities control fluxes of water, heat and carbon between the surface and the atmosphere is important for improving atmospheric models and for understanding the impacts of land use change. This project will use data from the measurement campaign Land-Atmosphere Interactions in the Iberian Semi-Arid Environment and from numerical experiments with large eddy simulation to investigate how local surface heterogeneities impact the partitioning of the surface energy budget and the development of the atmospheric boundary layer over a range of spatial temporal scales.