Soil water dynamics

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

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

Water holding capacity $W H C_{x y}$ [mm] and permanent wilting point $P W P_{x y}$ [mm] are derived by:

\begin{aligned} W H C_{x y} & = F_{W H C, x y} \cdot R D_{x y} \\ P W P_{x y} & = F_{P W P, x y} \cdot R D_{x y} \\ F_{W H C, x y} & = β_{S N D, W H C} \cdot S N D_{x y} + β_{S L T, W H C} \cdot S L T_{x y} + β_{C L Y, W H C} \cdot C L Y_{x y} + β_{O M, W H C} \cdot O M_{x y} + β_{B L K, W H C} \cdot B L K_{x y} \\ F_{P W P, x y} & = β_{S N D, P W P} \cdot S N D_{x y} + β_{S L T, P W P} \cdot S L T_{x y} + β_{C L Y, P W P} \cdot C L Y_{x y} + β_{O M, P W P} \cdot O M_{x y} + β_{B L K, P W P} \cdot B L K_{x y} \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 $W H C_{x y}$ [-]
$β_{S L T, W H C}$ relates silt content to fraction of soil filled with water at $W H C_{x y}$ [-]
$β_{C L Y, W H C}$ relates clay content to fraction of soil filled with water at $W H C_{x y}$ [-]
$β_{O M, W H C}$ relates organic matter content to fraction of soil filled with water at $W H C_{x y}$ [-]
$β_{B L K, W H C}$ relates bulk density to fraction of soil filled with water at $W H C_{x y}$ [cm³ g⁻¹]
$β_{S N D, P W P}$ relates sand content to fraction of soil filled with water at $P W P_{x y}$ [-]
$β_{S L T, P W P}$ relates silt content to fraction of soil filled with water at $P W P_{x y}$ [-]
$β_{C L Y, P W P}$ relates clay content to fraction of soil filled with water at $P W P_{x y}$ [-]
$β_{O M, P W P}$ relates organic matter content to fraction of soil filled with water at $P W P_{x y}$ [-]
$β_{B L K, P W P}$ relates bulk density to fraction of soil filled with water at $P W P_{x y}$ [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.