|Title (Primary)||Parametric soil water retention models: a critical evaluation of expressions for the full moisture range|
|Author||Madi, R.; de Rooij, G.H.; Mielenz, H.; Mai, J.|
|Journal||Hydrology and Earth System Sciences|
|UFZ wide themes||RU1;|
|Abstract||Few parametric expressions for the soil water
retention curve are suitable for dry conditions. Furthermore,
expressions for the soil hydraulic conductivity curves associated with
parametric retention functions can behave unrealistically near
saturation. We developed a general criterion for water retention
parameterizations that ensures physically plausible conductivity curves.
Only 3 of the 18 tested parameterizations met this criterion without
restrictions on the parameters of a popular conductivity curve
parameterization. A fourth required one parameter to be fixed.
We estimated parameters by shuffled complex evolution (SCE) with the objective function tailored to various observation methods used to obtain retention curve data. We fitted the four parameterizations with physically plausible conductivities as well as the most widely used parameterization. The performance of the resulting 12 combinations of retention and conductivity curves was assessed in a numerical study with 751 days of semiarid 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 of the soil hydraulic parameterization that ideally does not only rely on goodness of fit to static soil water retention data but also on hydraulic conductivity measurements.
Parameter fits for 21 soils showed that extrapolations into the dry range of the retention curve often became physically more realistic when the parameterization had a logarithmic dry branch, particularly in fine-textured soils where high residual water contents would otherwise be fitted.
|Persistent UFZ Identifier||https://www.ufz.de/index.php?en=20939&ufzPublicationIdentifier=19904|
|Madi, R., de Rooij, G.H., Mielenz, H., Mai, J. (2018):
Parametric soil water retention models: a critical evaluation of expressions for the full moisture range
Hydrol. Earth Syst. Sci. 22 (2), 1193 - 1219