Hydrological science has often been too compartmental in the past mainly because the majority of scientists dealing with the water cycle tend to look at hydrology from a limited perspective of their own discipline. Recently, interdisciplinary approaches linking hydrological processes to plant physiology, land-atmosphere interactions, forest ecology, geomorphology, and biogeochemical cycles have emerged and are finding their way to traditional hydrological models. Coupling the modeling of hydrology with the related processes can improve the representation of underlying physics and mechanisms at different space-time levels. Specifically, at the mesoscale [i.e. at the basin scale; between 100 to 10,000 km2], such a multi-disciplinary approach could possibly overcome the fragmentary view of the system offered by sub-disciplines that address only a subset of processes occurring at a particular scale.
At the plot (25-2500 m2) and small watershed scale, the hope is that physically based approaches developed at the process-level scale can become a viable alternative to extensively used mechanism "representations" that are detached from space-time characteristics of catchment hydrology in terms of observed energy fluxes, soil moisture, temperature, etc. The characterization of previously missing physical process descriptions or linkages can hopefully lead to better understanding of catchment hydrology and modeling/upscaling capabilities.

At the mesoscale, reliable observations for most of the water fluxes and system state variables (e.g., soil moisture) at the spatial resolutions between 1 and 4 km cannot be made. Consequently, models can only be validated indirectly at larger scales by remote sensing or at micro-scales by field experiments. The task is then to develop reliable procedures to down/upscaling mesoscale modeling results to the level at which the observations are made. The challenge is to develop new approaches, sensors, and models that can do that seamlessly.

In both approaches hydrological models should be seen as tools to test hypotheses and process understanding rather than only used for prediction purposes of a single constituent, such as outlet streamflow.

This session invites contributions from various types of research at different scales (from plot- to small-watershed to mesoscale) that have lead to more comprehensive insights into hydrological behavior or explanation of patterns and elucidation of “difficult/persistent” problems. Numerical, experimental, and theoretical studies that investigate water and energy fluxes, the role of vegetation on hydrological processes, and the combination of model with remote sensing or field measurement data at the different scales are sought. Investigations of new connections or feedbacks between hydrology-related topics and surface-subsurface hydrological states and flows are also welcome.