Predicting how earth surface systems respond to changing land uses and climate conditions is one of our key challenges and requires us to develop innovative experimental, observational and modelling methods. This is in particular true for hydrological, biogeochemical and geomorphic development of catchments, which are driven by external changes of climate and weather conditions as well as internal processes operating at multiple scales. Recent developments in artificial catchment research have clearly highlighted the difficulties we have in predicting hydrologic and geomorphic responses during the early stages of catchment evolution. For example, small scale processes at the soil surface not easily predictable determined the catchment scale rainfall-runoff behaviour in an established well-monitored artificial catchment in an unforeseen way. This strongly supports a multidisciplinary approach allowing us to assess and predict interacting processes at multiple spatial and temporal scales and to identify feedbacks that will drive systems transition.

Accordingly the key questions to be addressed in this session are: (i) How can we develop experiments, which allow us to identify processes and process interaction responsible for sudden shifts in states; (ii) How can we observe and determine early warning signs of state transitions of natural or managed catchments that are beyond our ability to perform well-controlled experimentation and (iii) How can we model state transitions in a meaningful way with an appropriate level of complexity linked to data and observations. During this session we invite contributions that will help us to understand state transitions preferably at the catchment scale focussing on hydrological, biogeochemical and geomorphic responses to environmental perturbations. More specifically we are seeking oral and poster contributions in the following areas:
· Experimental systems such as artificial catchments undergoing rapid transitions in their hydrological, biogeochemical and geomorphic behaviour
· Innovative data analysis of observation of transient systems that indicate sudden shifts in their state from all areas in hydrology, biogeosciences, geomorphology, and soil systems science.
· Modelling studies that specifically address the analysis and predictions of transient earth surface systems, with a focus on the identification of feedback mechanisms contributing to the state transitions.
We welcome studies on the development of artificial catchments with respect to the water balance, vegetation, biogeochemical cycles, and geomorphology. Other examples for highly transient systems may stem from landscapes disturbed by anthropogenic activities such as mining or urban encroachment as well as landscape development after natural events such as volcano eruptions, wild fires or flooding.