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Effect of potential evapotranspiration estimates on effective parameters and performance of the MIKE SHE-code applied to a medium-size catchment

Abstract:

The effect of the method of calculating a time series of crop potential evapotranspiration (ET<inf>p</inf>) on both the model performance and the magnitude of the main effective parameters of a distributed hydrological model was assessed on the basis of an independent multi-calibration. The ET<inf>p</inf> was estimated as a function of the reference evapotranspiration (ET<inf>o</inf>) by means of a crop coefficient approach. Three methods for deriving ET<inf>o</inf> estimates were used in modelling a medium size catchment in Belgium: (A) Food and Agriculture Organisation (FAO) FAO-24 standard approach; (B) FAO-24 approach but used with coefficients, for both the wind and the Stefan-Boltzmann equations, differing from the standard formulation; and (C) FAO-56 standard approach. For assessing the performance of the estimation approaches, the point scale ET<inf>o</inf> outputs of the generation methods were compared to local point scale ET<inf>o</inf> guidelines derived from previous research. The outputs of generation method B and of the generation method C showed a close agreement with the local point scale ET<inf>o</inf> guidelines. Their effect (to a catchment scale) on the performance of the hydrological model also seemed to be comparable. The best model performance was obtained by using the higher ET<inf>o</inf> data generated by method A. The research also revealed a significant dependency of some of the effective parameters on the different ET<inf>p</inf> estimates; especially of those parameters related to the computation of the actual evapotranspiration (ET<inf>act</inf>). © 2002 Elsevier Science B.V. All rights reserved.