Application of hydrologic similarity concepts is prevalent in hydrology. We utilize similarity to transfer information from one catchment to another and to understand underlying catchment processes based on previously studied catchments. Catchment-scale models and parameterizations or regionalization of statistical, physical and (or) climatological catchment properties are often used to generalize results beyond individual catchments based on similarity/dissimilarity. These concepts also form the basis for classification frameworks. A wide variety of approaches – ranging from statistically- to physically-based methods – for quantifying hydrologic similarity or dissimilarity between catchments have been introduced and tested in the literature. However, synthesis and critical assessment of these methods remains an outstanding challenge.

Looking at catchments as closely coupled hydro-geo-eco system reveals a highly organized architecture that is characterized by typical patterns, of topography, soil and vegetation and self-similar flow networks at all scales. These patterns, biota and networks organise storage of water, nutrients and energy, energy exchange of the catchment as well as mass export (water, sediments) across large scale gradients. Understanding catchment organisation might be key for developing a common framework for hydrologic similarity as well as for building more realistic dynamic catchment models that balance the necessary complexity with greatest possible simplicity and to address the problem of transient hydro-geo-ecosystems.

This session welcomes a combined discussion on ideas and approaches that further our understanding of both hydrologic similarity and catchment organization.