Environmental change can be observed at different spatial and temporal scales and encompasses various system properties, such as climate, land use, topography and soil properties. Some of the changes that we are facing are predictable to a certain extent (e.g. the rise in surface temperature) and some are direct consequences of human activities (e.g. the degree of deforestation, landscape fragmentation). The WAVE project aims to improve our understanding of the interactions between vegetation and the water balance in ecosystems, in order to enable better predictions of some of the consequences of land use and environmental change for both ecosystem servies and water resources.The proposed project will advance ecohydrological understanding and modelling in three directions, (a) by improving quantitative representation of physical constraints on the functioning of plants through targeted lab and field experiments; (b) by developing a community-based model evaluation framework enabling the hydrological community to progressively build on each others modelling efforts and rigorously evaluate models against cutting edge observational data; and (c) by implementing physical constraints and optimality hypotheses in models at different scales and testing them against observations in a consistent and transparent way.