Deriving accurate estimates of reference evapotranspiration is required for water resources management, irrigation water requirement computations and successfully hydrological modelling. The Food and Agriculture Organization of the United Nations (FAO) recommended the Penman‐Monteith equation as the standard for estimating reference evapotranspiration. Alternative method for application at sites where only air temperature measurements are available is the Hargreaves‐Samani equation. The main objective of this study is to investigate the possibility for application of Hargreaves‐Samani equation in Alpine area for computing daily reference evapotranspiration. An evaluation of the Hargreaves‐Samani equation and its modifications proposed in literature is made by comparing daily estimates with Penman‐Monteith results at 51 meteorological stations in the upper Po river basin (Italy) and the Rhone river basin (Switzerland). Significant error was encountered in all methods based on Hargreaves‐Samani equation. A relationship for adjusting Hargreaves‐Samani coefficient based on local elevation is proposed, calibrated and validated. The resulting modified Hargreaves‐Samani equation showed a significant reduction of error for estimating daily reference evapotranspiration. The proposed equation is not intended for replacement of Penman‐Monteith method but to be used for application in Alpine river when only air temperature data are available.

Modified Hargreaves-Samani equation for the assessment of reference evapotranspiration in Alpine river basins

RAVAZZANI, GIOVANNI;CORBARI, CHIARA;MANCINI, MARCO
2012-01-01

Abstract

Deriving accurate estimates of reference evapotranspiration is required for water resources management, irrigation water requirement computations and successfully hydrological modelling. The Food and Agriculture Organization of the United Nations (FAO) recommended the Penman‐Monteith equation as the standard for estimating reference evapotranspiration. Alternative method for application at sites where only air temperature measurements are available is the Hargreaves‐Samani equation. The main objective of this study is to investigate the possibility for application of Hargreaves‐Samani equation in Alpine area for computing daily reference evapotranspiration. An evaluation of the Hargreaves‐Samani equation and its modifications proposed in literature is made by comparing daily estimates with Penman‐Monteith results at 51 meteorological stations in the upper Po river basin (Italy) and the Rhone river basin (Switzerland). Significant error was encountered in all methods based on Hargreaves‐Samani equation. A relationship for adjusting Hargreaves‐Samani coefficient based on local elevation is proposed, calibrated and validated. The resulting modified Hargreaves‐Samani equation showed a significant reduction of error for estimating daily reference evapotranspiration. The proposed equation is not intended for replacement of Penman‐Monteith method but to be used for application in Alpine river when only air temperature data are available.
2012
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11311/634045
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