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. The CloudRoots field experiment was designed to obtain acomprehensive observational dataset that includes soil, plant, andatmospheric variables to investigate the interaction between a heterogeneousland surface and its overlying atmospheric boundary layer at the sub-hourlyand sub-kilometre scale. Our findings demonstrate the need to includemeasurements at leaf level to better understand the relations betweenstomatal aperture and evapotranspiration (ET) during the growing season atthe diurnal scale. Based on these observations, we obtain accurateparameters for the mechanistic representation of photosynthesis and stomatalaperture. Once the new parameters are implemented, the model reproduces thestomatal leaf conductance and the leaf-level photosynthesis satisfactorily.At the canopy scale, we find a consistent diurnal pattern on thecontributions of plant transpiration and soil evaporation using differentmeasurement techniques. From highly resolved vertical profile measurements of carbon dioxide (CO2) and other state variables, we infer aprofile of the CO2 assimilation in the canopy with non-linearvariations with height. Observations taken with a laser scintillometer allowus to quantify the non-steadiness of the surface turbulent fluxes during therapid changes driven by perturbation of photosynthetically active radiationby cloud flecks. More specifically, we find 2 min delays between thecloud radiation perturbation and ET. To study the relevance of advection andsurface heterogeneity for the land–atmosphere interaction, we employ acoupled surface–atmospheric conceptual model that integrates the surface andupper-air observations made at different scales from leaf to the landscape.At the landscape scale, we calculate a composite sensible heat flux byweighting measured fluxes with two different land use categories, which isconsistent with the diurnal evolution of the boundary layer depth. Usingsun-induced fluorescence measurements, we also quantify the spatialvariability of ET and find large variations at the sub-kilometre scalearound the CloudRoots site. Our study shows that throughout the entiregrowing season, the wide variations in stomatal opening and photosynthesislead to large diurnal variations of plant transpiration at the leaf, plant,canopy, and landscape scales. Integrating different advanced instrumentaltechniques with modelling also enables us to determine variations of ET thatdepend on the scale where the measurement were taken and on the plantgrowing stage.

CloudRoots: integration of advanced instrumental techniques and process modelling of sub-hourly and sub-kilometre land–atmosphere interactions