Hydrological scientists are faced with the problem (common to many of the field sciences) of complexity at small scales leading to relative simplicity (the hydrology) at large scales. Little or no success has been gained in relating the former to the latter. Hydrologists will be increasingly forced to think in terms of spatial complexity and spatial pattern but the available tools of analysis are not adequate to accommodate such information. A basis for a new paradigm is laid in a perceptual model of catchment response, leading to an initial conceptual framework incorporating spatial integration and predictive uncertainty.-from Author