We propose an analytical method to identify the importance of different components of the hydrological cycle during storm events in humid temperate catchments. Hydrological response is the result of numerous complex interactions among hydrological inputs (e.g., rain and radiation) and landscape properties (e.g., vegetation, topography, and soil properties) through a number of hydrological processes at the land surface. The multitude of such interactions makes it difficult to identify the dominant controls on catchment response and on catchment-to-catchment variability within any particular river basin. The method we develop expresses the variability of catchment-averaged storm runoff rates in terms of the space and time variability of hydrological inputs and landscape properties, with particular emphasis on the processes of runoff generation and runoff routing. Given suitable data on rainfall, land surface, and channel network properties, the equations we obtain can be used to indicate the dominant sources of between-catchment variability in storm runoff. We illustrate the use of this method for a 10-hour storm over a 420 km2 study catchment. ¿ 1999 American Geophysical Union