Author(s): Aj Collados-Lara; Cl Ramon; F. Huertas; L. Rico Jorge; Ep Sanchez-Canete; Fj Rueda

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Keywords: Evaporation in reservoirs; Eddy-covariance; Pan evaporation; Hargreaves method; Penman-Monteith method

Abstract: Reservoirs and their water storage are essential in areas where water resources are scarce, as is the case in the Mediterranean Basin. There, evaporation becomes one of the most important components of the water balance due to the associated eventual high-magnitude water losses. These rates might become higher in the future in the context of climate change. In general, reservoir managers estimate evaporation from evaporation pans and/or indirect methods that assess potential evapotranspiration or reference evapotranspiration from temperature and/or radiation-based equations. However, these equations may not be accurate enough for a specific case study or where the pan coefficient, which measures the ratio of reservoir to pan evaporation rates, is not evaluated. This can introduce errors in the estimation of evaporation rates and the water balance of the reservoir. Eddy-covariance is currently considered the most direct technique available for measuring evaporation. In this study, we compare direct daily evaporation measurements using eddy-covariance equipment installed on an existing floating platform in Cubillas Reservoir (south Spain) with pan evaporation rates measured by the reservoir's managers as well as with theoretical formulations of the Hargreaves potential evapotranspiration method and the Penman-Monteith reference evapotranspiration method. The Hargreaves and the Penman-Monteith methods overestimate annual evaporation by 196 mm (17%) and 356 mm (31%) respectively. The pan evaporation method underestimate evaporation by 216 mm (19%). In the light of these results it would be convenient to use a pan coefficient of 0.89 instead 0.72. It has important implications for the management of the Cubillas reservoir.

DOI: https://doi.org/10.3850/978-90-833476-1-5_iahr40wc-p1574-cd

Year: 2023