The fact that persistent spatial organization in catchments exists inspired many scientists to speculate whether this is a manifestation of self-reinforcing co-development due to an underlying organizing principle. Spatial organization of catchments manifests through different fingerprints and affects different processes:

  • Hillslope scale spatial organization of soil types manifests in a typical arrangement of soil types along the topographic gradient. This is of key importance for overland flow, sediment yields, water availability for evaporation, and temporal stability of soil moisture patterns.
  • Spatially organized variability at the pedon scale (within a soil type) is reflected in a spatial correlation of soil hydraulic properties, which translates into spatially correlated storage and recharge.
  • Soils and unconsolidated rock are veined with connected networks of preferential flow paths either created by biota (worms, rodents, roots) or by abiotic processes (shrinkage cracks, pipes, rills). Activated preferential flow networks allow for high mass flows even at small driving gradients and thus dominate export and redistribution of water and matter across many scales.

Jim Dooge was to our knowledge the first hydrologist who realized that spatial organization alongside with stochastic heterogeneity leads to complex hydrological behavior at intermediate scales (5-250 km2). Dooge argued that these are systems of organized complexity; being already too large and heterogeneous to be treated in a reductionist deterministic manner, but yet too small for characterizing their behavior using first and second order statistics. The latter is possible at larger scales of organized simplicity. Despite great progress made since Dooge’s pioneering work in hillslope hydrology and the conceptualization of organized simplicity, we feel still pretty “naked” at the intermediate scale of organized complexity. There is little agreement neither on how fieldwork-based understanding should be reflected in catchment models to improve hydrological predictions, nor on how an appropriate model structure should look like, nor on what the controls are that determine the emergent behavior.

The objective of the Chapman Conference is to foster the development of a holistic framework to explore and understand how catchment organization, which is ultimately the fingerprint of the past hydrological and landscape formation processes, controls terrestrial water and energy cycles in intermediate scale catchments. We intend to contribute to achieving this goal via three closely related topical conference sessions.

Topic 1) Organizing principles, catchment structure, and catchment functioning – is there a connection?
Here, we aim at linking the how to the why question by synthesizing testable hypotheses that could explain why spatial organization has evolved as a fingerprint of past catchment flows of water and energy. Ecology, fluvial geomorphology, and thermodynamics offer a large set of candidate organizing principles. We will discuss to which extent we can test their value for improving hydrological predictions (how) and what the requirements are regarding data collection and models structures in order to accomplish this goal.
Keynote by Bill Dietrich, Professor of Earth and Planetary Sciences, University of California, Berkeley, USA.
Invited talk by Patricia Saco, Senior Lecturer, School of Engineering, The University of Newcastle, Australia.

Topic 2) New experimental concepts to search for functional landscape entities and to explore their controls on catchment functioning
Is catchment organization reflected in the existence of functional units that compile catchment functioning? The idea of functionally similar landscape entities is not new but still an appealing concept to link stratified observations, landscape, and model structures. We will focus 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.
Keynote by Brian McGlynn, Professor of Watershed Hydrology and Biogeosciences, Nicholas School of Environment, Duke University, USA.
Invited talk by Ilja van Meerveld, Assistant Professor, Faculty of Earth and Life Sciences, VU University Amsterdam, The Netherlands.

Topic 3) Reducing physical and structural bias in catchment models: necessary complexity versus parsimony
Here we focus on how to develop parsimonious model structures relying on observable quantities. Special emphasis is on explicit representation of landscape controls of “gradients and resistances” determining water and energy flows across scales. What is the minimum necessary complexity so that organizing principles become testable? Which metrics shall be used to test whether such models allow consistent predictions of distributed dynamics (gained within novel strategies addressed in topic 2) and integral flows?
Keynote by Jasper Vrugt, Assistant Professor, The Henry Samueli School of Engineering, Department of Civil and Environmental Engineering, , University of California, Irvine , California, USA.
Invited talk by Luisa Hopp, Research Associate, Department of Hydrology, University of Bayreuth, Germany.