Performance Evaluation of Models That Describe the Soil Water Retention Curve between Saturation and Oven Dryness

Abstract

The objective of this work was to evaluate eight closed‐form unimodal analytical expressions that describe the soil‐water retention curve across the complete range of soil water contents. To meet this objective, the eight models were compared in terms of their accuracy (RMSE), linearity (coefficient of determination, R2, and adjusted coefficient of determination, R2adj), and prediction potential. The latter was evaluated by correlating the model parameters to basic soil properties. Retention data for 137 undisturbed soils from the Unsaturated Soil Hydraulic Database (UNSODA) were used for the model comparison. The samples showed considerable differences in texture, bulk density, and organic matter content. All functions were found to provide relatively realistic fits and anchored the curve at zero soil water content for the coarse‐textured soils. The performance criteria were similar when averaged across all data sets. The criteria were found to be statistically different between the eight models only for the sandy clay loam soil textural class. An analysis of the individual data sets separately showed that the performance criteria were statistically different between the models for 17 data sets belonging to six different textural classes. We found that the Khlosi model with four parameters was the most consistent among different soils. Its prediction potential was also relatively good due to significant correlation between its parameters and basic soil properties.

Parametric soil water retention models: a critical evaluation of expressions for the full moisture range

“…(4) is met. The asymptotic dry end that was removed in the unimodal version by Khlosi et al (2008) (Eq. S14a) remains though, limiting its applicability in dry soils.…”

“…Numerical solvers of Richards' equation for water flow in unsaturated soils require these curves as descriptors of the soil in which the movement of water should be calculated. Many parametric expressions for the retention curve and fewer for the hydraulic conductivity have been developed for that purpose (see the Supplement, Leij et al, 1997;Cornelis et al, 2005;Durner and Flühler, 2005;Khlosi et al, 2008;Assouline and Or, 2013).…”

“…In doing so, we add to the existing body of comparative studies of parametric retention curves by explicitly including the associated hydraulic conductivity curves according to these conductivity models. Papers introducing new parameterizations of the soil water retention curve as well as reviews of such parameterizations typically show the quality of the fit to soil water retention data (e.g., van Genuchten, 1980;Rossi and Nimmo, 1994;Cornelis et al, 2005;Khlosi et al, 2008). The role of these parameterizations is to be used in solutions of Richards' equation, usually in the form of a numerical model.…”

Folyadék-visszatartás, folyadékvezetés és porozitás összefüggései vízzel és/vagy szerves folyadékkal telített talajokban I. Folyadék-visszatartó képesség — Szemle

“…FAYER és SIMONS (1995) a kapillárisok által meghatározott folyadékvisszatartó-képesség tartományt a szigmoid jellegű KOSUGI (1996: K1) függvénnyel, míg az adszorpció által meghatározott folyadékvisszatartó-képességet CAMPBELL és SHIOZAWA (1992: CS) logaritmikus függvényével jellemezte. A teljes nyomástar-tomány folyadékvisszatartó-képességének elemzéshez azonban ez esetben is szük-séges a görbék közötti "átfedés" tanulmányozása, és az egyenletek "harmonizálása" (a kapilláris értelmezés szerint "nagy" nyomáson (10 4 kPa) a kis kapillárisok telítet-tek, míg a film-áramlást leíró elmélet változó vastagságú filmet feltételez a telítetlen kapillárisokban (FAYER & SIMON, 1995;KHLOSI et al, 2008).…”

Review of Soil Water Retention Characteristic (SWRC) Models between Saturation and Oven Dryness

“…Many of these models have been reported successful only for certain parts of SWRC (e.g. wet or dry parts), soil textures, soil horizons, regions of the world, or limited soil stress history [6]. These models contain shape parameters known as hydraulic parameters.…”