The evolution of modern hydrology (from watershed to continent in 30 years)

The purpose of this paper is to describe hydrology to a scientifically-literate audience of non-hydrologists and to highlight its evolution over the last 30 years from a field focused on engineering problems at the scale of the small watershed to one dealing with global-scale issues which demand a geophysical perspective. The Ralph M. Parsons Laboratory at MIT has been one of the leaders of this evolution, and the illustrations presented of things that (some) hydrologists do are drawn primarily from recent work done there. These include: introduction of the concept of hydrologic scale along with its definition, significance and estimation; the sub-grid scale parametrization of precipitation and vegetation in atmospheric GCMs; precipitation recycling; and completion of the land surface-atmosphere feedback loop for moisture at climatic time scales.