The current form and functioning of landscapes are the result of the landscape-scale co-evolution of biological, physical and chemical processes in the past, constrained increasingly by anthropogenic activity. Hydrological functioning is a fundamental part of these complex interactions across spatio-temporal scales. Thus, studies linking system organisation (e.g. emerging spatial structures of vegetation, geology, topography) with hydrological processes can provide important insights to advance our understanding of the flow and storage of energy, water and solutes at different scales. In order to allow for scaling and transfer of concepts in space and time, a critical analysis of the information in our data and the concepts behind our experiments and models is required. An improved understanding of the basic principles controlling soil-vegetation-atmosphere interactions and landscape co-evolution is necessary in order to produce reliable predictions of hydrological processes under non-stationary system conditions.

The availability, consistency and transparency of measurement data form the very foundation for building this understanding. Open access to these datasets ensures reproducibility of the published findings, adds visibility to the datasets and facilitates tests for theory development. Besides access to the data, methods to combine diverse datasets for integral analyses are essential.

This is a joint special issue in HESS and ESSD. We encourage submission of contributions to both journals as companion papers (data paper in ESSD and analyses of these data in HESS) or to either one. The special issue is open for all submissions within the previously described scope. As such we invite contributions which e.g. cover • hypothesis-driven design of multiscale and interdisciplinary measurements, • organisation, analysis and sharing of such observational data and metadata, • theoretical considerations of spatio-temporal organisation of hydrological functioning from plot to landscape scale, • physiographic controls on fundamental hydrological catchment functions (i.e. water collection, storage, mixing and release), • identifying controls and feedbacks of water and energy exchange and storage, • juxtaposition of concurrent conceptualisations of hydrological processes, • anthropogenic constraints on the hydrological functioning of landscapes, • identification of dominant processes, effective scales and representative ensembles, and • hydrological functioning under non-stationary system conditions.