Catchments are organised systems: their behaviour mostly results of typical patterns of topography, soils, and vegetation and this organisation of catchment components controls the storage and release of water and nutrients at the short and medium term. The behaviour of catchments also shows longer-term dependencies to storage in aquifers, lakes and man-made reservoirs, which significantly affects the variability of hydrological response in time, across multiple spatial and temporal scales.

Understanding catchment organization and assessing its memory is critical for (i) creating catchment models that balance necessary complexity with possible simplicity, (ii) understanding the degree of similarity between catchments, with the prospect of developing hydrological theories that are transferable in space and/or time, (iii) understanding and predicting the potential impact of environmental changes on hydrological response in a changing environment, and (iv) better managing and operating water resources systems, water quality plans or flood protection systems.

This session invites contributions on:
. the degree of model complexity needed to characterize catchment processes and response,
. new approaches to assess the memory of catchments,
. multi-catchment analysis of the degree of similarity in climate, landscape, and hydrology,
. methods and case studies identifying controls on the residence time of water and solutes in contrasting landscapes,
. the relative effects of climate, landscape and human interventions on catchment response,
. methods assessing the impact of land use change on catchment response,
. the uncertainties involved in the identification of dominating processes and hydrologic response behaviour,
. studies of historic climate variability to quantify catchment memory,
. regionalisation of catchment memory through catchment organisation description and its underlying organizing principle,
. the measure (i.e., quantification) of human impacts and the consequent change on catchment response behaviour and similarity,
. case studies on flood-rich/drought-rich and flood-poor/drought-poor sequences,
. methods exploiting catchment memory to improve hydrological models, discharge and nutrient prediction, and evaluation of water resources systems.

Note that from the point of view of the 23 Unsolved Problems in Hydrology initiative, this session will contribute to addressing six problems: n°5, n°6, n°8, n°9, n°14 and n°22.