Benchmarking test of empirical root water uptake models

Abstract

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.

Relationship between root water uptake and soil respiration: A modeling perspective

“…Comparisons between models of soil water fluxes using these different expressions for root water uptake have been presented by De Willigen et al [] and Camargo and Kemanian [] in some virtual experiments. On the other hand, Santos et al [] evaluated the capability of some empirical models to imitate the water extraction distribution under varying environmental conditions from numerical simulations of a detailed physical model.…”

Impact of capillary rise and recirculation on simulated crop yields

“…Also, soil and water management practises like ploughing and irrigation were not considered. Furthermore, the rooting pattern needed a more detailed analysis; we applied an exponential decrease in root density and compensation of root uptake according to Jarvis (1989Jarvis ( , 2011 but the macroscopic root water uptake concept was still simple and may require a more detailed analysis (Dos Santos et al, 2017). Another item we neglected is the preferential flow of water by the occurrence of non-capillary sized macropores (Bouma, 1981;Feddes et al, 1988), which is especially relevant in clay soils.…”

An extension of water retention and conductivity functions to dryness

“…Soil WR and HC are the fundamental properties to predict water flow in soils and its linkage to key processes in the vadose zone, such as root water uptake (Dos Santos, De Jong Van Lier, Van Dam, & Bezerra, ) and the fate of solutes and pollutants (Šimunek, Van Genuchten, & Kodešová, ). These soil physical properties are usually represented by equations relating pressure head h , soil water content θ and hydraulic conductivity K .…”

“…Soil WR and HC are the fundamental properties to predict water flow in soils and its linkage to key processes in the vadose zone, such as root water uptake (Dos Santos, De Jong Van Lier, Van Dam, & Bezerra, 2017) and the fate of solutes and pollutants (Šimunek, Van Genuchten, & Kodešová, 2018). These soil physical properties are usually represented by equations relating pressure head h, soil water content θ and hydraulic conductivity K. The commonly used equations are those proposed by Brooks and Corey (1964), Campbell (1974), Durner (1994), Groenevelt and Grant (2004), Kosugi (1996), Van Genuchten (1980), and Peters and Durner (2008), and their parameters are calibrated using observed data in laboratory or field experiments.…”