Although considerable effort has gone into assessing and projecting climatic change, continental-scale analyses of trends in only one component of the hydrologic cycle—precipitation—have been described. With few exceptions [see Zektser and Loaiciga, 1993], assessments of temporal variations in runoff, evaporation, and soil water storage have been neglected, to some degree because of a lack of adequate observational data.
On a regional basis, have there been any changes in seasonal patterns of streamflow in the United States? If so, are these changes consistent with documented variations in other hydroclimatic variables? To answer these questions, we examined a set of climate-sensitive streamflow data recently collected by the U.S. Geological Survey. This data set covers the years 1941–1988 and presents data from 559 gaging stations across the conterminous United States.