Submitted Abstract
Catchments are spatially organized systems with complex dynamics. The persistent spatial patterns in catchments around the world have inspired many scientists to speculate whether this organization is a manifestation of self-reinforcing co-development processes due to some underlying organizing principle. Spatial organization of catchments manifests itself in different ways and through different processes:•Hillslope scale spatial organization of soil types in the form of catenary sequences along topographic gradients. •Spatially organized soil hydraulic properties. •Organized connected networks of preferential flow paths, either created by biota (worms, rodents, roots) or by abiotic processes (shrinkage cracks, pipes, rills).The spatial organization of catchments is of key importance for overland flow, sediment yields, nutrient transport, water availability for evaporation, hillslope-stream connectivity and the temporal stability of soil moisture patterns. Such spatial organization also translates into a dynamic organization of spatially correlated storage and recharge affecting bio-geochemical and ecological processes in a catchment.The purpose of this Chapman conference (http://chapman.agu.org/catchments/) was to foster the development of a holistic framework to explore and understand catchment organization and how it controls terrestrial water and energy cycles in intermediate scale catchments. The conference was organized around three main topics: Topic 1Organizing principles, catchment structure and catchment functioning – is there a connection? Here, we aimed at linking the ‘how’ to the ‘why’ question by generating testable hypotheses that could explain why spatial organization has evolved as a fingerprint of past catchment flows of water and energy. We discussed to which extent we can test the value of different organizing principles e.g. from ecology, fluvial geomorphology or thermodynamics for improving hydrological predictions and the related requirements on data collection and model structures.Topic 2 New experimental concepts to search for structurally/functionally similar landscape units and to explore their controls on catchment functioning Is catchment organization reflected in the existence of typical, structurally and functionally similar ‘least landscape elements’ that can advantageously be used to understand and predict catchment behavior? Or is landscape rather a random conglomerate of its constituents? The idea of typical least landscape elements is not new but still an appealing concept, as it can be the basis for the design of parsimonious yet representative monitoring networks, and to define the structure and elements of dynamical models to adequately represent these landscapes. We focused on novel multi-method and multi-sensor strategies to search for such functional entities in intermediate scale catchments and, if they exist, to learn in an exemplary manner whether and how structural features control functional characteristics and hence catchment functioning.Topic 3Adequate catchment models: necessary complexity versus parsimonyHere we focused on how to identify and develop adequate (for a given purpose) catchment models, which relates to both the representation of physical processes and landscape structure in the model. Special emphasis was on explicit representation of landscape controls of “gradients and resistances” determining water and energy flows across scales. Also, what is the minimum necessary model complexity to allow for self-organization to occur? This is the prerequisite for organizing principles to become testable hypotheses. Which metrics shall be used to test whether such models allow consistent predictions of observed dynamics (gained from monitoring strategies addressed in topic 2)?