Cálculo da evaporação de albufeiras de grande regularização do sul de Portugal =Calculation of evaporation in high regulation reservoirs in southern of Portugal

摘要

The identification of the more robust and portable methodologies of evaporation calculation in a Mediterranean climate with Atlantic proximity, bearing in mind the comprehensive description of the conditioning mechanisms of free water surface evaporation, is the main objective of the present study. To meet this goal, estimates of evaporation in nine reservoirs spread throughout the southern Portuguese territory for the period from 2002 to 2006 were used as case studies. Since one of the main drawbacks to the correct determination of the evaporation component in lakes and reservoirs comes from the use of evaporation-related meteorological parameters measured outside the water surface, a network of floating sets was design to retrieve meteorological information on the water in all the nine reservoirs both from meteorological and water thermal conditions. A group of different rationales, from empirical and semi-empirical models to a onedimensional lake model (FLake), were used for the estimation of evaporation on both daily and monthly time scales. Each model performance was checked by comparing its estimates with the ones coming from the energy balance equation. Since for the water planning and management of lakes and reservoirs side the main contribution coming from this study would be the delivery of robust and portable evaporation calculation methods, especial attention was devoted to straight forward methods such as the mass transfer and the evaporation-pan estimates. Thus pan and mass transfer coefficients, with regional representativeness stemming from areal considerations in the latest, were generated. Last but not least, to consolidate the use of energy balance as a standard for cross checking and also to detect how the regional estimation techniques would behave in short periods of time, an intensive field measurement session was set up using the most complete method of measurement: the eddy-correlation flux.