Catchment water deficits in the 21st century

The objective of this paper is to provide a general theory of the manner in which the water resources of a catchment shift from surplus to deficit and the means by which water resource institutions can manage or reverse this shift. The approach combines the languages of hydrology and the social sciences. After defining the concepts of catchment water surplus and deficit, an account is given of how a river basin may shift from one to the other as its output per head and population expand. Twelve possible options to confront such a shift are reviewed. The paper discusses the global significance of these issues and ends with a general testable hypothesis as a basis for fieldwork.