| (𝒶) | Parameter defined ad hoc by Van Genuchten, 1980 as given in [42] as the reciprocal of capillary pressure | [M−1∙L T2] |
| (α) | Total porosity also given as (Φ), the complement of the ratio (ρs/ρp). | [1] |
| (α), (as), (aw) | Thermal diffusivity defined as the ratio of the thermal conductivity to the volumetric heat capacity. Where (s) denotes the bulk soil and (w) denotes “as regards the water”. It has the SI derived unit of (m2∙s−1). | [L2∙T−1] |
| (βο) | Brutsaert equation parameter defined ad hoc by Brutsaert [17], as given in Assouline, 2013, as given in [15] | [1] |
| (β) | Shape constant in Haverkamp, 1994 equation, as given in [24] |
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| (γ) | Vapour-liquid/Interfacial tension/Surface tension defined as the elastic tendency of a fluid surface which makes it acquire the least surface area possible Speight, 2020, as given in [41] | [M∙T−2] |
| (γ) | Proportionality constant in Haverkamp, 1994 equation, as given in [24] |
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| (ΔΤ) | Initial temperature difference | [T] |
| (δ). | Interpolation parameter of Haverkamp, 1990 equation, as given in [23] |
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| (η) | Dynamic or absolute viscosity defined as a measure of water’s internal resistance | [M∙L−1∙T−1] |
| (Θ) | Degree of saturation (see also effective saturation) | [1] |
| (θ) | Moisture content/soil-water content/water retention defined as the ratio of the mass of water contained in the pore spaces of soil or rock material, to the solid mass of particles in that material, expressed as a percentage ASTM D653-20, given in [4] | [L3∙L−3] |
| (θi) | Initial moisture content defined as the moisture volume percentage in soils before irrigation or raining | [L3∙L−3] |
| (θm) | Maximum moisture content defined as the maximum value of the liquid content as given above | [L3∙L−3] |
| (θo), (θn) | Volumetric water content in final & initial states according to Haverkamp, 1994 equation, as given in [24] | [L3∙L−3] |
| (θr) | Residual moisture content is the quantity of water retained in a residual soil (as percent) | [L3∙L−3] |
| (θs) | Saturated moisture content defined as the liquid content value in a saturated soil | [L3∙L−3] |
| (λ) | Thermal conductivity defined as the proportionality factor in Fourier’s Law that represents the ability of soil to conduct heat and is equivalent to the thermal flux per unit temperature gradient. In SI units, thermal conductivity is measured in watts per meter-kelvin (W∙m−1⋅K−1). Thermal conductivity often denoted, λ, or κ). (λ) is referring to the liquid of our interest. | [M∙L∙T−3∙Θ−1] |
| (λs) | Thermal conductivity where (s) denotes the bulk soil | [M∙L∙T−3∙Θ−1] |