Increasing Evapotranspiration from the Conterminous United States

Abstract

Recent research suggests that evapotranspiration (ET) rates have changed over the past 50 years; however, some studies conclude ET has increased, and others conclude that it has decreased. These studies were indirect, using long-term observations of air temperature, cloud cover, and pan evaporation as indices of potential and actual ET. This study considers the hydrological cycle more directly and uses published precipitation and stream discharge data for several large basins across the conterminous United States to show that ET rates have increased over the past 50 years. These results suggest that alternative explanations should be considered for environmental changes that previously have been interpreted in terms of decreasing large-scale ET rates.