(dgrain) Mean soil grain diameter defined as the average estimated value of the grained soil diameter [L] (dinner) Diameter of the inner ring of a double ring infiltrometer [L] (dpore) Diameter mean pore size [L] (dring) Diameter of the ring of the infiltrometer [L] ( $\frac{\text{d}T}{\text{d}z}$ ) Temperature/thermal gradient vertical direction, within boundaries [L−1∙Θ] f(r) Volume frequency defined ad hoc by Pereira & Arson, 2017 as given in [35] [1] (g) Gravitational acceleration/gravitational constant defined as the acceleration on an object caused by the force of gravitation [L∙T−2] (Go) Ground heat flux defined as energy received by the soil to heat it per unit of surface and time [M∙T−3] g(r) Pore radius distribution function by Kosugi, 1997, as given in [27] [1] (H) Sensible heat (flux) defined as the energy moving from one system to another that changes its temperature rather than changing its phase [M∙T−3] (H) Head of ponding defined as the depth of the ponded water above the surface [L] (h) Soil water pressure head/Hydrostatic pressure defined by the hydrostatic pressure expressed as the height of a column of water that the pressure can support at the point of measurement United States Geological Survey—USGS, Glossary of Hydrologic Terms, given in [50]. Hydrostatic pressure is the pressure exerted by the weight of water at any given point in a body of water at rest (American Geosciences Institute—AGI, Glossary of Geology), given in [48]. See also matric suction [L] (hc) Capillary pressure head defined as the pressure difference between a fluid of a higher pressure and another fluid of a lower. It is common practice to express the pressure as an equivalent of a water height Encyclopedia of Soil Science [L] (hc(e)) Capillary (entry) pressure head defined as the pressure (in column height) to enter the non-wetting phase to the largest size of the pores of a porous medium Liu et al., 2014, as referred in [30] [L] (i) Hydraulic gradient/Darcy slope defined as the inclination of the line joining different pressure heads. A line joining the points of highest elevation of water in a series of vertical open pipes rising from a pipeline in which water flows under pressure (ASCE) [1] J(s) Capillary pressure function defined ad hoc by (Leverett, 1941) as the relationship between the capillary pressure and the pore structure, as given in [29] [1] (K) Hydraulic conductivity/Coefficient of permeability defined as a proportionality constant (in Darcy's Law), relating hydraulic gradient to specific discharge which for an isotropic medium and homogeneous fluid, equals the volume of water at the existing kinematic viscosity that will move in unit time under a unit hydraulic gradient through a unit area measured at right angles to the direction of flow [L∙T−1] (kf), (kintr), (K) Intrinsic permeability/absolute permeability/specific permeability defined as the measure of the relative ease with which a porous medium can transmit a fluid under a potential gradient and is a property of the medium alone Lohman, 1972, as given in [31] and United States Geological Survey—USGS, Glossary of Hydrologic Terms, given in [50] the measurement of the permeability, or ability to flow or transmit fluids through a rock, conducted when a single fluid, or phase, is present in the rock Schluberger Oil Field Glossary, as given in [49] [L2] (Ki) Initial unsaturated hydraulic conductivity defined as a quantitative measure of an unsaturated soil's ability to transmit water when subjected to a hydraulic gradient at the initial stage of wetting [L∙T−1] (Kr) Relative hydraulic conductivity defined ad hoc by Mualem’s 1976 as given in [32], by the given equation (Kr) = $\left(\theta -{\theta }_{r}\right)/\left({\theta }_{s}-{\theta }_{r}\right)$ [1] (Ks) Fluid solubility defined as the property of a fluid substance called solute to dissolve in a solid, liquid or gaseous solvent [1] (Ks) Saturated hydraulic conductivity defined as a quantitative measure of a saturated soil's ability to transmit water when subjected to a hydraulic gradient or the easiness with which pores of a saturated soil permit water movement. [L∙T−1]