Soil water dynamics

The dynamics of the soil water content in the rooting zone $W_{t}$ [mm] is described by:

\begin{aligned} W_{t + 1} & = W_{t} + P_{t} - A E T_{t} - R_{t} \\ A E T_{t} & = min (W_{t}, E_{t} + T R_{t}) \\ R_{t} & = max (0 mm, W_{t} + P_{t} - A E T_{t} - W H C) \\ E_{t} & = \frac{W_{t}}{W H C} \cdot P E T_{t} \cdot [1 - min (1, \frac{L A I_{t o t, t}}{3})] \\ T R_{t} & = max (0, \frac{W_{t} - P W P}{W H C - P W P}) \cdot P E T_{t} \cdot min (1, \frac{L A I_{t o t, t}}{3}) \\ L A I_{t o t, t} & = \sum_{s = 1}^{S} L A I_{t s} \\ L A I_{t s} & = B_{A, t s} \cdot s l a_{s} \cdot \frac{l b p_{s}}{a b p_{s}} \cdot 0.1 \end{aligned}

Water holding capacity $W H C$ [mm] and permanent wilting point $P W P$ [mm] are derived by:

\begin{aligned} W H C & = F_{W H C,} \cdot R D \\ P W P & = F_{P W P,} \cdot R D \\ F_{W H C,} & = β_{S N D, W H C} \cdot S N D + β_{S L T, W H C} \cdot S L T + β_{C L Y, W H C} \cdot C L Y + β_{O M, W H C} \cdot O M + β_{B L K, W H C} \cdot B L K \\ F_{P W P,} & = β_{S N D, P W P} \cdot S N D + β_{S L T, P W P} \cdot S L T + β_{C L Y, P W P} \cdot C L Y + β_{O M, P W P} \cdot O M + β_{B L K, P W P} \cdot B L K \end{aligned}

Equations and parameter values for water holding capacity and permanent wilting point are based on Gupta and Larson (1979).

$β_{S N D, W H C}$ relates sand content to fraction of soil filled with water at $W H C$ [-]
$β_{S L T, W H C}$ relates silt content to fraction of soil filled with water at $W H C$ [-]
$β_{C L Y, W H C}$ relates clay content to fraction of soil filled with water at $W H C$ [-]
$β_{O M, W H C}$ relates organic matter content to fraction of soil filled with water at $W H C$ [-]
$β_{B L K, W H C}$ relates bulk density to fraction of soil filled with water at $W H C$ [cm³ g⁻¹]
$β_{S N D, P W P}$ relates sand content to fraction of soil filled with water at $P W P$ [-]
$β_{S L T, P W P}$ relates silt content to fraction of soil filled with water at $P W P$ [-]
$β_{C L Y, P W P}$ relates clay content to fraction of soil filled with water at $P W P$ [-]
$β_{O M, P W P}$ relates organic matter content to fraction of soil filled with water at $P W P$ [-]
$β_{B L K, P W P}$ relates bulk density to fraction of soil filled with water at $P W P$ [cm³ g⁻¹]

Visualization

derive permanent wilting point and water holding capacity from soil characteristics:

julia

change_water_reserve(
;
    container,
    water,
    precipitation,
    PET,
    WHC,
    PWP
)

Simulates the change of the soil water content in the rooting zone within one time step.

julia

transpiration(; container, water, PWP, WHC, PET, LAItot)

Simulates transpiration from the vegetation.

julia

evaporation(; water, WHC, PET, LAItot)

Simulate evaporation of water from the soil.

julia

input_WHC_PWP!(; container)

Derive walter holding capacity (WHC) and permanent wilting point (PWP) from soil properties.