Environmental modelling in the hydrological cycle: What the client needs?

This paper summarizes expert and user views in some of the fields which are of interest to the Environment Agency. Models have been specifically designed to fulfil the needs of particular functions such as water resources, flood defence, and water quality. There are trends towards models serving more than one function and operating to represent the 'natural' processes in an entire catchment or the wide range of parameters influencing the habitat at one point. Model evolution is likely to be driven partly by the client's requirements (based in turn on more stringent legislation, economics, public expectation and new phenomena) and partly by advances in computational power. The recent focus on holistic treatment of catchments and their multi-functional issues may stimulate the development of the relatively new distributed, linked models more than their single-function counterparts.