Soil

Maximum liquid water content in a soil layer below the freezing point, following the supercooled-soil-water freezing-point depression treatment of Niu and Yang (2006). Below T_f, liquid coexists with ice via the matric-potential / latent-heat balance of Oleson et al. (2010) Eq. 4.58; above T_f, the layer holds the fully-saturated maximum Δz·θ_sat·ρ_liq. Migrated from UrbanCanopy.jl@9200edd4 src/roof_wall_road_snow_temperatures.jl:949 (`FreezingPointDepression` @component). Parameterized as observed-only: T_i, θ_sat, Δz, ψ_sat, B_i, ρ_liq are inputs (parameters); w_liq_max is the algebraic output.

Hydraulic conductivity at a soil-layer interface as a Clapp-Hornberger function of the average volumetric water content and porosity of the two adjacent layers, scaled by the unfrozen fraction. Implements Oleson et al. (2010, CLM Tech Note Ch. 5) Eq. 5.69 (interface conductivity) with the frozen-fraction multiplier of Eq. 5.70. Migrated from UrbanCanopy.jl@9200edd4 src/hydrology.jl:1053 (`InterfaceHydraulicConductivity` @component). Observed-only: all eight inputs are parameters and k_h is given by a single algebraic equation.

Per-layer phase-change adjustment for ice/liquid water redistribution and temperature correction in the urban canopy thermal column. Migrated from UrbanCanopy.jl@9200edd4 src/roof_wall_road_snow_temperatures.jl:686 (`PhaseChangeAdjustment` @component). Implements Oleson et al. (2010, CLM Tech Note Ch. 4) Eqs. 4.60–4.65: given the excess/deficit energy H_i (W/m²) available for phase change in layer i (from `PhaseChangeEnergy`), recompute ice mass w_ice^{n+1}, liquid water mass w_liq^{n+1}, and layer temperature T^{n+1}. Melting occurs when H_i > 0 (surplus energy melts ice up to available mass); freezing occurs when H_i < 0 (deficit energy freezes liquid water). Residual energy H_res = H_i - L_f*(w_ice^n - w_ice^{n+1})/Δt that cannot drive further phase change adjusts the layer temperature. The upstream MTK component is parameterized at construction time by `layer_type ∈ {:interior, :top}`. The two variants share equations 1–4 (Eqs. 4.60–4.64) and differ only in Eq. 4.65 (temperature correction): the :top variant divides by (1 - (Δt/(c_i*Δz_i))*dh_dT) to account for the linearized surface-heat-flux feedback; the :interior variant uses the denominator = 1 (no surface feedback). Both variants are unified here via a dimensionless switch parameter `is_top` (0.0 = interior, 1.0 = top), identical to the unification strategy used by the sibling `PhaseChangeEnergy` component. NOTE: the migration-tracker entry for this component listed `blocking_gap: other:discretization-plan` citing line :1227, but that line belongs to `RoadHeatConduction` (a separate non-exported helper function). `PhaseChangeAdjustment` itself is a pure algebraic MTK `@component` with no PDESystem or MOLFiniteDifference — this migration is unblocked.

Per-layer energy excess/deficit available for phase change in the urban canopy thermal column. Migrated from UrbanCanopy.jl@9200edd4 src/roof_wall_road_snow_temperatures.jl:496 (`PhaseChangeEnergy` @component). Implements Oleson et al. (2010, CLM Tech Note Ch. 4) Eq. 4.59 for layer i: the imbalance between net heat fluxes (Crank-Nicholson average of times n and n+1) and the thermal storage required to bring the layer to the freezing point T_f. When H_excess > 0 the layer has surplus energy that can melt ice; when H_excess < 0 it has deficit energy that can freeze liquid water. The upstream MTK component is parameterized at construction time by `layer_type ∈ {:interior, :top}`. The two variants share a Crank-Nicholson bottom-flux contribution and the thermal-storage term but differ in the upper boundary: the :top variant adds a surface heat flux `h_n + dh_dT*(T_f - T_i_n)` (Eq. 4.59 for i = snl+1), while the :interior variant subtracts the upper-interface Crank-Nicholson flux `α_CN*F_im1_n + (1-α_CN)*F_im1_np1` (Eq. 4.59 for i > snl+1). Both variants are merged here into a single algebraic equation switched by an `is_top` dimensionless parameter (0.0 = interior, 1.0 = top); both upstream test fixtures pass against this merged form with the appropriate parameter set.

Soil hydraulic properties for an urban-canopy pervious-road soil column following Section 5.3.1 of Oleson et al. (2010, CLM4 Tech Note). Computes five Clapp-Hornberger / Cosby-style properties from the soil sand and clay fractions and the local volumetric water content: saturated hydraulic conductivity k_sat (Eq. 5.70), porosity θ_sat (Eq. 5.71), Clapp-Hornberger exponent B (Eq. 5.72), saturated matric potential ψ_sat (Eq. 5.74), and matric potential ψ (Eq. 5.73, clamped on both sides). Migrated from UrbanCanopy.jl@9200edd4 src/hydrology.jl:322 (`SoilHydraulicProperties` @component). Observed-only: all three inputs are parameters and all five outputs are given by single algebraic equations.

Thermal conductivity and volumetric heat capacity for soil layers in the pervious-road column of the urban canopy thermal solver. Migrated from UrbanCanopy.jl@9200edd4 src/roof_wall_road_snow_temperatures.jl:75 (`SoilThermalProperties` @component). Implements Oleson et al. (2010, CLM Tech Note Ch. 4 §4.3): thermal conductivity follows Farouki (1981) using the Kersten-number method (Eqs. 4.77-4.82); volumetric heat capacity follows de Vries (1963) (Eqs. 4.85-4.86). Parameterized as observed-only: pct_sand, pct_clay, θ_sat, θ_liq, T_i, w_ice, w_liq, Δz are inputs (parameters); λ_s, λ_sat, λ_dry, ρ_d, S_r, K_e, λ_soil, c_s, c_soil are algebraic outputs. The component carries two temperature-conditioned `ifelse` branches: λ_sat and K_e switch between frozen (T_i < T_f) and unfrozen (T_i ≥ T_f) regimes, while λ_soil falls back to λ_dry whenever S_r drops below a small numerical threshold.

Total volumetric soil water content from per-layer liquid-water and ice masses, following Oleson et al. (2010, CLM Tech Note Ch. 5) Eq. 5.137. Migrated from UrbanCanopy.jl@9200edd4 src/hydrology.jl:1091 (`SoilWaterContentCalc` @component). Parameterized as observed-only: w_liq, w_ice, Δz are inputs (parameters); θ_i is an algebraic output combining both phases via their respective densities.

Layer-averaged equilibrium volumetric water content (θ_E, Eq. 5.101) and equilibrium matric potential at the layer node (ψ_E, Eq. 5.106) for a single soil layer, following Oleson et al. (2010, CLM4 Tech Note Ch. 5, §5.3.2.1, Eqs. 5.98–5.106). θ_E is fully saturated (θ_sat) when the water table is above the layer (z_v < z_h_upper), otherwise is computed by integrating the hydrostatic-equilibrium Clapp-Hornberger profile across the layer, clamped to [0, θ_sat]. ψ_E is derived from the Brooks-Corey inverse relation with a 1% saturation floor and a hard lower bound at ψ_min = −10⁵ m to prevent numerical underflow. Migrated from UrbanCanopy.jl@9200edd4 src/hydrology.jl:509 (`SoilWaterEquilibrium` @component). Note: the migration-tracker row for this component carried the blocking_gap `other:discretization-plan` because the row description mentioned an in-file Richards-equation PDE at src/hydrology.jl:674. Inspection shows that PDESystem lives in a separate non-`@component` helper function (`RichardsEquation`) and is not part of `SoilWaterEquilibrium`, which is a plain two-equation algebraic `@component`. No discretization plan is needed.

Soil water flux at the interface between two adjacent soil layers, computed from Darcy's law with the Zeng and Decker (2009) equilibrium-potential correction (Oleson et al. 2010, CLM4 Tech Note Eq. 5.88). q = -k_interface * ((ψ_upper - ψ_lower) + (ψ_E_lower - ψ_E_upper)) / (z_lower - z_upper), positive upward. Migrated from UrbanCanopy.jl@9200edd4 src/hydrology.jl:471 (`SoilWaterFlux` @component). Observed-only: the seven inputs are parameters and q is given by a single algebraic equation.

Water table depth z_v as a function of unconfined-aquifer water storage W_a and the depth of the bottom soil interface z_h_bottom. Implements Oleson et al. (2010) CLM Tech Note Eq. 5.146 (p. 143) with hard clamps at z_v_min = 0.05 m and z_v_max = 80 m. Migrated from UrbanCanopy.jl@9200edd4 src/hydrology.jl:743 (`WaterTableDepth` @component). Observed-only: z_h_bottom and W_a are parameters and z_v is given by a single algebraic equation.