Evapotranspiration predictions: a comparison among GLEAMS, Opus, PRZM-2, and RZWQM models in a humid and thermic climate

Environmental fate models are increasingly used to evaluate potential impac ts of agrochemicals on water quality to aid in decision making. However, er rors in predicting processes like evapotranspiration (ET), which is rarely measured during model validation studies, can significantly affect predicti ons of chemical fate and transport. This study compared approaches and pred ictions for ET by GLEAMS, Opus, PRZM-2, and RZWQM and determined effects of the predicted ET on simulations of other hydrology components. The ET was investigated for 2 years of various fallow-corn growing seasons under sprin kler irrigation. The comparison included annual cumulative daily potential ET (ETp), actual ET, and partitioning of total ET between soil evaporation (E-s) and crop transpiration (E-t). When measured pan evaporation was used for calculating ETp (the pan evaporation method), Opus, PRZM-2, and RZWQM p redicted 74, 65, and 59%, respectively, of the 10-year average ET reported for a nearby site. When the energy-balance equations were used for calculat ing ETp (the combination methods), GLEAMS, Opus, PRZM-2, and RZWQM predicte d 84, 105, 60, and 72% of the reported ET, respectively. The pan evaporatio n method predicted a similar amount of ET to the combination methods for ba re soil, but predicted less ET when both E-s and E-t occurred. RZWQM reason ably predicted partitioning of ET to E-s, while GLEAMS and Opus over-predic ted this partitioning. A close correlation between soil water storage in th e root zone and ET suggests that accurate soil water content predictions we re fundamental to ET predictions. (C) 1999 Elsevier Science Ltd. All rights reserved.