Estimación de la tasa de evaporación desde embalse en Andalucía

Abstract

Evaporative losses from reservoirs are an important element of the hydrological balance, that must be considered in the planning and exploitation stages, especially in arid and semi-arid climates. In the present work, the average annual evaporation in a total of 78 andalusian reservoirs of more than 5 hm3 has been estimated by three semi-empirical methods using daily data from the automatic network of meteorological stations in Andalusia (period of 21 hydrological years). To this end, a computer routine was implemented for the systematized treatment of data along with a previous protocol for the depuration and completion of the meteorological series used. Of the methods applied, the FAO Penman-Monteith method seems to offer the most realistic values, with intermediate results to those obtained from the rest of methods, including previous studies. According to this method, the annual evaporation rate ranges between a minimum of 1.151 mm/yearand a maximum of 1.425 mm/year, with an average value of 1.297 mm/year for all the reservoirs. The Penman method appears to significantly overestimate evaporation (between 1.559 and 1.817 mm/year, with a mean value of 1.687 mm/year). Hargreaves on the other hand provides statistics similar to those obtained by the first method but does not present a correlation with it owing to the reduced number of variables considered. Besides, evaporation has not shown a significant dependence on altitude, contrary to previous studies. Finally, it should be noted that the results obtained with the FAO Penman-Monteith equation refer to the reference evapotranspiration (ETo), which, despite constituting a useful approximation for studying the phenomena of water transfer to the atmosphere, must be contrasted with direct or balance methods.