Revisiting hydraulic hysteresis based on long‐term monitoring of hydraulic states in lysimeters

Abstract

Hysteretic processes have been recognized for decades as an important characteristic of soil hydraulic behavior. Several studies confirmed that wetting and drying periods cannot be described by a simple functional relationship, and that some nonequilibrium of the water retention characteristics has to be taken into account. A large number of models describing the hysteresis of the soil water retention characteristic were successfully tested on soil cores under controlled laboratory conditions. However, its relevance under field conditions under natural forcings has rarely been investigated. In practice, the modeling of field soils usually neglects the hysteretic nature of soil hydraulic properties. In this study, long-term observations of water content and matric potential in lysimeters of the lysimeter network TERENO-SoilCan are presented, clearly demonstrating the hysteretic behavior of field soils. We propose a classification into three categories related to different time scales. Based on synthetic and long-term monitoring data, three different models of hysteresis were applied to data sets showing different degrees of hysteresis. We found no single model to be superior to the others. The model ranking depended on the degree of hysteresis. All models were able to reflect the general structure of hysteresis in most cases but failed to reproduce the detailed trajectories of state variables especially under highly transient conditions. As an important result we found that the temporal dynamics of wetting and drying significantly affects these trajectories which should be accounted for in future model concepts.

Scales of Water Retention Dynamics Observed in Eroded Luvisols from an Arable Postglacial Soil Landscape

“…Despite the present absence of experimental evidence for these explanations, the disentangling of the field data could provide ideas for including the intraseasonal dynamics of soil hydraulic properties in the simulation of the soil water flow (e.g., Alletto et al, 2015). Similarly, Hannes et al (2016) stated that better model representations of the complex dynamics of soil water retention were needed that included a concept of hydraulic nonequilibrium and temporal dynamics of soil structure that lead to changes in hydraulic properties. In this sense, long‐term effects of soil erosion have to be considered; soil profile truncation and a continuous incorporation of subsoil material through plowing in the topsoil (or conversely the deposition of colluvium) may gradually change textural, structural, and soil chemical and biological properties.…”

“…Thus, for the main wetting and drying curves, a factor of two was suggested, which was sometimes used as default value in numerical models of soil water flow. The modeling of hysteretic water retention was tested in field studies (e.g., Basile et al, 2003; Canone et al, 2008); however, these models were not able to fully reproduce the dynamic behavior of water retention data under in situ conditions (Hannes et al, 2016). Thus, Hannes et al (2016) suggested grouping observed water retention dynamics in three categories: the hydraulic nonequilibrium, the quasi‐nonequilibrium situation, and the soil structure dynamics.…”

“…The modeling of hysteretic water retention was tested in field studies (e.g., Basile et al, 2003; Canone et al, 2008); however, these models were not able to fully reproduce the dynamic behavior of water retention data under in situ conditions (Hannes et al, 2016). Thus, Hannes et al (2016) suggested grouping observed water retention dynamics in three categories: the hydraulic nonequilibrium, the quasi‐nonequilibrium situation, and the soil structure dynamics. These concepts could still need more information on the relations of categories to relevant processes in the field and additional pedological factors that affected soil properties (e.g., manifested in erosion history), for instance, textural changes and profile truncation resulting from tillage erosion.…”

Scale Issues in Soil Hydrology

“…The latter can be considered as hydraulic nonequilibrium with a pretty long time scale of equilibration. An impressive collection of long‐term monitoring data for water content and water potential showing hysteresis and hydraulic nonequilibrium was presented by Hannes et al (2016), which is discussed further below. When relating measurements of water content and water potential, the different support volume of the measurements needs to be considered.…”

Infiltration from the Pedon to Global Grid Scales: An Overview and Outlook for Land Surface Modeling

“…In general, there are many soil characteristics broadly related to soil composition and structure (including macro‐ and biopores) and also to exogenic processes, including water repellency, wetting and drying, swelling and shrinkage, air entrapment, freeze–thaw, thermal gradients, impermeable layers, and anthropogenic perturbations (e.g., tillage, harvesting) that impact infiltration and runoff at the point scale (see Young and Crawford [2004] and Hannes et al [2016], for example).…”