Evaluation of three complementary relationship evapotranspiration models by water balance approach to estimate actual regional evapotranspiration in different climatic regions

Three evapotranspiration models using the complementary relationship approach for estimating areal actual evapotranspiration were evaluated and compared in three study regions representing a large geographic and climatic diversity: NOPEX region in Central Sweden (cool temperate, humid), Baixi catchment in Eastern China (subtropical, humid), and the Potamos tou Pyrgou River catchment in Northwestern Cyprus (semiarid to arid). The models are the CRAE model of Morton, the advection– aridity (AA) model of Brutsaert and Stricker, and the GG model proposed by Granger and Gray using the concept of relative evapotranspiration (the ratio of actual to potential evapotranspiration). The calculation was made on a daily basis and comparison was made on monthly and annual bases. The study was performed in two steps: First, the three evapotranspiration models with their original parameter values were applied to the three regions in order to test their general applicability. Second, the parameter values were locally calibrated based on the water balance study. The results showed that (1) using the original parameter values all three complementary relationship models worked reasonably well for the temperate humid region, while the predictive power decreases in moving toward regions of increased soil moisture control, i.e. increased aridity. In such regions, the parameters need to be calibrated. (2) Using the locally calibrated parameter values all three models produced the annual values correctly. For the monthly values there was a time shift for the appearance of maximum monthly values between the evapotranspiration model estimations and water balance calculations, and the drier the region, the larger the difference. Further examination of the water balance components showed that while the actual evapotranspiration is controlled by several hydrometeorological factors in warmer and drier months the soil moisture is the dominating factor. q 2004 Elsevier B.V. All rights reserved.