The impact of environmental change is likely to bring about a response in hydrological conditions at a site. The water balance at any location is controlled by climate, vegetation cover and soil properties. Any change in the external climate or in the internal structure of the soil/vegetation system will be reflected in changes in site hydrology. This may involve changes in evaporation, in soil moisture levels, and in the amount of runoff from the site. At sites where snow forms an important component of the precipitation, climate change may have particularly important effects. Monitoring of hydrological variables in ECN may therefore provide a sensitive indicator of environmental change. Continuous discharge measurements (summarised every 15 minutes) are made.