The issue of scales and nonlinear physical, chemical and biological processes is of fundamental importance in hydrology. The questions of how such processes are organized in space and time across a range of scales, how different processes interact at different scales, and how observations at one scale are related to those at another have profound implications for our ability to predict hydrologic cycle components. Answering these questions, in view of the undergoing environmental changes at all scales, requires concerted theoretical, modeling, and experimental efforts. Such efforts are undertaken by research groups around the world. This session is devoted to reporting research results on all aspects of scales and scaling in both groundwater and surface hydrology, including hydrometeorology and ecohydrology. Scaling research topics on hydrologic processes on scales ranging from laboratory to hillslope to small (e.g. urban) basins to regions and continents to entire Earth are all appropriate. Contributions of both scientific and engineering aspects of scaling research and applications are welcome. It is Convenors intention to approach this complex issue in a broad way in order to encompass different scales both in time and space including interactions between nonlinear hydrologic processes at different scales. Posters focusing on a specific scale, either for surface or groundwater processes and their modeling and observations, are also welcome.