Pan Evaporation Trends in Dry and Humid Regions of the United States

Abstract

Decreasing pan evaporation trends in many regions of the world have been viewed as evidence of a decrease in the terrestrial evaporation component of the hydrologic cycle. However, some researchers suggest that the relationship between pan evaporation and terrestrial evaporation depends on the environment in which the measurements are recorded and that pan evaporation trends run counter to trends in terrestrial evaporation in some climates. To determine whether evidence of this kind of relationship exists in the observational record, pan evaporation trends were compared with precipitation trends in eight regions within the United States. To the extent that warm-season precipitation can be used as an indicator of surface evaporation, these results support the view that pan evaporation and actual evaporation can be inversely related.