EVAPORATION TRENDS OVER THE UNITED STATES AND THE FORMER USSR

Observed decreases in pan evaporation over most of the United States and the former USSR during the post-WWII period, if interpreted as a decrease in actual evaporation, are at odds with increases in temperature and precipitation over Northern Hemisphere extratropical land areas. Using parallel observations of actual and pan evaporation at five Russian, one Latvian, and one U.S. experimental sites, we recalibrate trends in pan evaporation to make them more representative of actual evaporation changes. After applying this recalibration, pan evaporation time series over southern Russia and most of the United States reveal an increasing trend in actual evaporation during the past forty years.