As the Earth’s population increases and a changing climate brings about changes in the natural environment, stresses develop in natural and social habitats. In particular, changes in the availability, quality and variability of water supplies, coupled with a period of increasing demand for water, cause hydrologic forcing in many different disciplines. This hydrologic forcing and consequent water-related decisions have profound impacts on the social and ecological environment. These impacts and their feedbacks create an unprecedented opportunity for significant new interdisciplinary science themes for hydrology. These will encompass a continuum of spatial scales from a single catchment to entire continents. The science of hydrology has been in the forefront of these issues but much work remains to be done for the development of scientific content in the interface between hydrology and the climate change, biology, chemistry and social sciences