Our understanding of runoff generation processes at the hillslope and catchment scale is often hampered by the complexity of hydrological systems due to the interactions of multiple external and internal factors. Annual and seasonal variations in climatic forcing or wetness conditions often lead to changes in hillslope and catchment states and a switch in the dominant controls on hydrological responses or travel time distributions. Contrasting behaviours are typically found when thresholds and other non-linear effects occur. For instance, differences in wetness conditions may result in changing directions in hysteretic storage/runoff loops or lead to the activation of subsurface flow pathways that dramatically increase streamflow. Studies to analyse these behaviours and unravel this complexity are critical to develop new concepts and theories that allow a more detailed description of the underlying hydrological processes and a more accurate conceptualization and prediction of hillslope and catchment functioning.

This session encourages contributions from experimental and modelling studies on:

i) The main controls on hillslope and catchment hydrological response in different wetness conditions, above/below precipitation thresholds or other hydrological thresholds;

ii) Hydrological processes leading to hysteretic and other non-linear relations (e.g. storage/runoff, concentrations/runoff);

iii) Changes in the spatial sources of runoff or dominant flow pathways at different times and under different conditions;

iv) Incorporation of thresholds and other non-linearities in hydrological models.