We aim to investigate the process of evapotranspiration (ET) in arid regions in northern and central Chile where evaporative water loss is confined to very localized regions in the landscape such as lagoons and in regions of irrigated agriculture. Different kinds of horizontal transport affect the climate of the desert. Between them, the marine advection of stratocumulus clouds, but also warm and dry air from the surrounding desert. This process enhances the evapotranspiration in these regions far more than what is expected from locally available net-radiation [1]. Traditional, single-equation models to determine ET, such as the FAO Penman-Monteith method [2], fail under these conditions. Yet, accurate ET estimates are essential to manage the scarcely available water which is needed for food production and supports unique the flora and fauna found in the shallow lagoons. The goal of the project is to understand the processes that drive the advection enhanced ET (AE-ET) through comprehensive field experiments combined with a land-atmospheric modelling hierarchy and observational data comparison. The first will include a novel technique that measures ET at a landscape scale (~km2): the optical microwave scintillate (OMS). The latter range from complex, regional 3D models to conceptual models. The outcome will be to extend parametrised ET formulations to include the AE-ET effect, to improve water management in the future.