Reference

Symbols and glossary

Symbols

Symbol	Meaning	Unit
h	pressure head (negative when unsaturated)	L
θ	volumetric water content	L³/L³
θ_r, θ_s	residual and saturated water content	–
S_e	effective saturation (θ − θ_r)/(θ_s − θ_r)	–
α, n, m	parameters of the van Genuchten function, m = 1 − 1/n	1/L, –, –
K, K_s, K_r	unsaturated, saturated and relative hydraulic conductivity	L/T, L/T, –
l	pore-connectivity parameter	–
C	water capacity dθ/dh	1/L
q	volumetric water flux (positive upward)	L/T
S	sink term (root water uptake)	1/T
T_p, T_a	potential and actual transpiration	L/T
E_p, ET_p	potential evaporation, potential evapotranspiration	L/T
α(h), ω, ω_c	water stress response function, water stress index, critical stress index	–
b(x)	normalized root distribution	1/L
LAI, SCF	leaf area index, soil cover fraction	–
T	temperature	°C
λ, λ₀	apparent thermal conductivity, conductivity without flow	M L T⁻³ K⁻¹
C_p, C_n, C_o, C_w	volumetric heat capacities of soil, solid phase, organic matter, water	M L⁻¹ T⁻² K⁻¹
c, s, g	concentrations in the liquid, solid and gas phases	M/L³, M/M, M/L³
ρ	bulk density	M/L³
D_L	longitudinal dispersivity	L
D_w, D_g	molecular diffusion coefficients in water and air	L²/T
K_s (Kd), η, β	sorption coefficients (Freundlich, Langmuir)	L³/M, L³/M, –
k_g	Henry's constant	–
μ, γ, μ'	first-order decay, first-order (chain) production, zero-order production	1/T, 1/T, M/L³/T
f	fraction of equilibrium sorption sites	–
θ_im	immobile water content	–
ω (α)	first-order mass-transfer coefficient	1/T
Pe, Cr	grid Peclet and Courant numbers	–
Φ, SSQ	objective function of the parameter estimation	–

Glossary

Term	Meaning
Atmospheric boundary condition	surface condition that switches between flux and head conditions according to precipitation, evaporation and the soil state (theory)
Breakthrough curve	concentration against time at a depth or in the outflow
Dual porosity	two pore regions, one of them immobile (theory)
Dual permeability	two pore domains that both conduct water (theory)
Fixed point	depth that is always a node of the mesh (soil profile)
hCritA	minimum pressure head allowed at the surface (dry limit of evaporation)
hCritS	maximum ponding depth at the surface before runoff
Hysteresis	dependence of θ(h) on the wetting and drying history (theory)
Material	soil layer type with its own parameters
Node	point of the finite element mesh
Observation node	node whose values are recorded at every time step
Print time	time at which profiles and balances are stored
Pumping effect	drift of hysteresis loops in models without memory of reversal points
Retention curve	relation θ(h), also water retention characteristic or soil water characteristic
Sub-region	part of the profile with its own mass balance
Time level	the end of a time step
Two-site sorption	sorption on equilibrium and kinetic sites (theory)

HYDRUS variable names

The tooltips name the variables of the HYDRUS-1D input files (e.g. hCritA, TolTh, dtMin, iKappa, lFluxOut, TauW), so that the HYDRUS-1D manual Šimůnek et al. (2009); Šimůnek et al. (2013) can be used alongside this help.

Literature cited in this topic

Šimůnek, J., M. Šejna, H. Saito, M. Sakai, and M. Th. van Genuchten (2009). The HYDRUS-1D Software Package for Simulating the One-Dimensional Movement of Water, Heat, and Multiple Solutes in Variably-Saturated Media, Version 4.08. HYDRUS Software Series 3, Department of Environmental Sciences, University of California Riverside, Riverside, CA, USA, 330 pp. https://www.pc-progress.com/en/Default.aspx?h1d-description
Šimůnek, J., M. Šejna, H. Saito, M. Sakai, and M. Th. van Genuchten (2013). The HYDRUS-1D Software Package for Simulating the One-Dimensional Movement of Water, Heat, and Multiple Solutes in Variably-Saturated Media, Version 4.17. HYDRUS Software Series 3, Department of Environmental Sciences, University of California Riverside, Riverside, CA, USA, 307 pp. https://www.pc-progress.com/en/Default.aspx?hydrus-1d

All sources: References.