Journal cover Journal topic
Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
doi:10.5194/hess-2016-168
© Author(s) 2016. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
25 Apr 2016
Review status
This discussion paper is under review for the journal Hydrology and Earth System Sciences (HESS).
Parametric soil water retention models: a critical evaluation of expressions for the full moisture range
Raneem Madi1, Gerrit Huibert de Rooij1, Henrike Mielenz2, and Juliane Mai3 1Dept. Soil Physics, Helmholtz Centre for Environmental Research – UFZ, Halle, Germany
2Institute for Crop and Soil Science, Julius Kühn-Institut – JKI, Braunschweig, Germany
3Dept. Computational Hydrosystems, Helmholtz Centre for Environmental Research – UFZ, Leipzig, Germany
Abstract. Of the many parametric expressions for the soil water retention curve, only a few are suitable for the dry 15 range. Furthermore, expressions for the soil hydraulic conductivity curves associated with these retention functions can exhibit non-physical behavior near saturation. We developed a general criterion that needs to be met by soil water retention parameterizations to ensure physically plausible hydraulic conductivity curves. Only three of the 18 tested parameterizations did not impose any restrictions on the parameters of the most popular conductivity curve parameterization, which includes three functions as special cases. One other retention function required one 20 conductivity parameter to be fixed.

We employed the Shuffled Complex Evolution parameter estimation method with the objective function tailored to various observation methods normally used to obtain retention curve data. We fitted the four parameterizations with physically plausible conductivities as well as the most widely used parameterization. We then compared the performance of the resulting 12 combinations of retention curve and conductivity curve in a 25 numerical study with 999 days of semi-arid atmospheric forcing applied to unvegetated, uniform, 1-m freely draining columns for four textures.

Choosing different parameterizations had a minor effect on evaporation, but cumulative bottom fluxes varied by up to an order of magnitude between them. This highlights the need for a careful selection procedure for the parameterization of the soil hydraulic properties that ideally does not only rely on goodness-of-fit to static soil 30 water retention data but also on observations of the hydraulic conductivity curve made during dynamic flow conditions.


Citation: Madi, R., de Rooij, G. H., Mielenz, H., and Mai, J.: Parametric soil water retention models: a critical evaluation of expressions for the full moisture range, Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-168, in review, 2016.
Raneem Madi et al.
Raneem Madi et al.
Raneem Madi et al.

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Short summary
Water flows through soils with more difficulty when the soil is dried out. Scant rainfall in desert may therefore result in a seemingly wet soil, but the water will often not penetrate deeply enough to replenish the groundwater. We compared the mathematical functions that describe how well different soils hold their water and found that only a few of them are realistic. The function one chooses to model the soil can have a large impact on the estimate of groundwater recharge.
Water flows through soils with more difficulty when the soil is dried out. Scant rainfall in...
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