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Hydrol. Earth Syst. Sci., 21, 473-493, 2017
https://doi.org/10.5194/hess-21-473-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
26 Jan 2017
Benchmarking test of empirical root water uptake models
Marcos Alex dos Santos1, Quirijn de Jong van Lier2, Jos C. van Dam3, and Andre Herman Freire Bezerra1 1Luiz de Queiroz, College of Agriculture, University of São Paulo, Piracicaba (SP), Brazil
2Center for Nuclear Energy in Agriculture, University of São Paulo, Piracicaba (SP), Brazil
3Department of Environmental Sciences, Wageningen University, the Netherlands
Abstract. Detailed physical models describing root water uptake (RWU) are an important tool for the prediction of RWU and crop transpiration, but the hydraulic parameters involved are hardly ever available, making them less attractive for many studies. Empirical models are more readily used because of their simplicity and the associated lower data requirements. The purpose of this study is to evaluate the capability of some empirical models to mimic the RWU distribution under varying environmental conditions predicted from numerical simulations with a detailed physical model. A review of some empirical models used as sub-models in ecohydrological models is presented, and alternative empirical RWU models are proposed. All these empirical models are analogous to the standard Feddes model, but differ in how RWU is partitioned over depth or how the transpiration reduction function is defined. The parameters of the empirical models are determined by inverse modelling of simulated depth-dependent RWU. The performance of the empirical models and their optimized empirical parameters depends on the scenario. The standard empirical Feddes model only performs well in scenarios with low root length density R, i.e. for scenarios with low RWU compensation. For medium and high R, the Feddes RWU model cannot mimic properly the root uptake dynamics as predicted by the physical model. The Jarvis RWU model in combination with the Feddes reduction function (JMf) only provides good predictions for low and medium R scenarios. For high R, it cannot mimic the uptake patterns predicted by the physical model. Incorporating a newly proposed reduction function into the Jarvis model improved RWU predictions. Regarding the ability of the models to predict plant transpiration, all models accounting for compensation show good performance. The Akaike information criterion (AIC) indicates that the Jarvis (2010) model (JMII), with no empirical parameters to be estimated, is the best model. The proposed models are better in predicting RWU patterns similar to the physical model. The statistical indices point to them as the best alternatives for mimicking RWU predictions of the physical model.

Citation: dos Santos, M. A., de Jong van Lier, Q., van Dam, J. C., and Freire Bezerra, A. H.: Benchmarking test of empirical root water uptake models, Hydrol. Earth Syst. Sci., 21, 473-493, https://doi.org/10.5194/hess-21-473-2017, 2017.
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Short summary
Some empirical root water uptake (RWU) models were assessed under varying environmental conditions predicted from numerical simulations with a detailed physical model. The widely used empirical RWU model by Feddes only performs well in scenarios of low RWU compensation. The RWU model by Jarvis cannot mimic the RWU patterns predicted by the physical model for high root length density scenarios. The two proposed models are more capable of predicting similar RWU patterns.
Some empirical root water uptake (RWU) models were assessed under varying environmental...
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