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Estimation of actual evapotranspiration by numerical modeling of water flow in the unsaturated zone: a case study in Buenos Aires, Argentina

Estimation de l’évapotranspiration vraie par modélisation numérique des écoulements dans la zone non saturée: une étude de cas à Buenos Aires, Argentine

Estimação da evapotranspiração real através de modelação numérica do fluxo de água na zona subsaturada: um caso de estudo em Buenos Aires, Argentina

Estimación de la evapotranspiración real a partir de la modelación del flujo en la zona no saturada: un estudio de caso en Buenos Aires, Argentina

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Abstract

A method is presented to estimate actual evapotranspiration (ETA) from potential evapotranspiration (ETP) by numerical modeling of water flow in the unsaturated zone. Water flow is described by the Richards equation with a sink term representing the root water uptake. Evaporation is included in the model as a Neumann boundary condition at the soil surface. The Richards equation is solved in a one-dimensional domain using a mixed finite element method. The values of ETA are obtained by applying a water stress factor to ETP to account for soil moisture changes during the simulation period. The proposed numerical model is used to estimate ETA in an experimental plot located in a flatland area in Buenos Aires (Argentina). Numerical results show that the proposed model is a useful tool for evaluating evapotranspiration under different scenarios.

Résumé

Une méthode d’estimation de l’évapotranspiration vraie (ETA) à partir de l’évapotranspiration potentielle (ETP) par modélisation numérique des écoulements dans la zone non saturée est proposée ici. Les écoulements sont décrits par l’équation de Richards avec un terme de rétention pelliculaire (skin) qui représente les prélèvements dans la zone racinaire. L’évaporation est entrée dans le modèle sous la forme d’une condition aux limites de type Neumann à la surface du sol. L’équation de Richards est résolue dans un domaine à une dimension au moyen d’une méthode aux éléments finis mixtes. Les valeurs d’ETA sont obtenues en appliquant un facteur de stress hydrique à l’ETP pour tenir compte des variations de l’humidité du sol au cours de la période simulée. Le modèle numérique proposé est utilisé pour estimer l’ETA sur un site expérimental dans une plaine de Buenos Aires (Argentine). Les résultats numériques montrent que le modèle proposé est un outil utile pour l’évaluation de l’évapotranspiration pour différents scénarios.

Resumo

É apresentado um método para estimar a evapotranspiração real (ETA) a partir da evapotranspiração potencial (ETP) através da modelação numérica do fluxo de água na zona subsaturada. O fluxo de água é descrito através da equação de Richards, com o termo rebaixamento a representar a água retirada pelas raízes. A evaporação é incluída no modelo como uma condição fronteira de Neumann à superfície do solo. A equação de Richards é resolvida num domínio unidimensional usando um método de elementos finitos misto. Os valores de ETA são obtidos através da aplicação de um factor de stress hídrico à ETP para representar as alterações na humidade do solo durante o período da simulação. O modelo numérico proposto é usado para estimar a ETA num local experimental localizado numa área plana em Buenos Aires (Argentina). Os resultados numéricos mostram que o modelo proposto é uma metodologia útil para a avaliação da evapotranspiração sob diferentes cenários.

Resumen

Se presenta un método que estima la evapotranspiración real (ETA) a partir de la evapotranspiración potencial (ETP) mediante el modelado del flujo de agua en la zona no saturada. El flujo de agua se describe mediante la ecuación de Richards con un término sumidero que representa el consumo de agua por parte de las raíces de las plantas. La evaporación se incluye en el modelo como una condición de borde de Neumann en la superficie del terreno. La ecuación de Richards se resuelve en un dominio unidimensional utilizando un método mixto de elementos finitos mezclados. Los valores de ETA se obtienen aplicando un factor de estrés hídrico a ETP que tiene en cuenta los cambios en la humedad del suelo durante el período de simulación. El método numérico propuesto se usa para estimar ETA en un sector experimental ubicado en una zona de llanura en Buenos Aires (Argentina). Los resultados numéricos muestran que el modelo es una herramienta útil para evaluar la evapotranspiración bajo diferentes escenarios.

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Acknowledgements

Support for this study was provided by CONICET (PIP 5126) and Agencia Nacional de Promoción Científica y Tecnológica (PICT 3–13376). Meteorological data were provided by Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata.

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Correspondence to Luis Guarracino.

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Cesanelli, A., Guarracino, L. Estimation of actual evapotranspiration by numerical modeling of water flow in the unsaturated zone: a case study in Buenos Aires, Argentina. Hydrogeol J 17, 299–306 (2009). https://doi.org/10.1007/s10040-008-0354-6

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