Complementary relationship between daily evaporation in the environment and pan evaporation

Daily actual evaporation observed locally is compared to daily pan evaporation to clarify and test the validity of the complementary relationship at this timescale. For this purpose, use was made of actual evaporation measurements at two sites, namely, in the Konza Prairie, Kansas, during the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment, and in the Little Washita River Basin, Oklahoma, as part of the Atmospheric Radiation Measurement Program. The corresponding pan evaporation data were obtained from nearby class A pan stations. The results of the analyses confirm the complementary relationship at this shorter timescale and lead to a procedure to estimate actual landscape evaporation by means of net radiation and pan evaporation data; they also provide support for the notion that even under conditions of decreasing incoming radiation, a negative trend in pan evaporation may still indicate a positive trend in landscape evapotranspiration.