Adaptation of the FAO´s method to assess real evapotranspiration in the SHALL hydrological simulation model

Abstract

Considering the predominance of the vertical direction in the exchange flows between hydrological components of the plain systems and, consequently, the preponderance of evapotranspiration as a process, an adaptation of the methodology proposed by FAO to the variables used by the SHALL hydrological model is presented. This model is suitable for continuous simulation in plain areas. The model is quasi-3D hydrodynamic, which considers the underground and surface components of water flows, together with the vertical flows towards the aquifer and the atmosphere. The model has been applied in open systems in the south of Santa Fe province and closed systems in the La Pampa province and is currently being implemented in depressed areas of Buenos Aires province. For the adaptation, an estimate of extreme effective saturation is proposed according to the moisture retention curves adjusted with Brooks-Corey formula. Following the guidelines of the publication FAO No. 56, an estimate of the effective limit saturation is presented for which, below it, the vegetal covers begin to restrict the supply of potential evapotranspiration, and the coefficient of hydric stress based on the calculated limit saturations, to estimate, finally, the real evapotranspiration based on variables contemplated by the SHALL model components.