Hydrology model configuration#

[See also the configuration details]

The hydrology model requires two simple initialisation values and then a set of hydrology constants one configuration section:

  • the initial soil moisture,

  • the initial groundwater saturation, and

  • the hydrology model constants ([hydrology.constants])

[hydrology]
static = false
initial_soil_moisture = 0.5
initial_groundwater_saturation = 0.9
p_wet_wet = 0.6
p_wet_dry = 0.3
rainfall_shape_parameter = 1.5
rainfall_scale_parameter = 1.0

[hydrology.constants]
soil_moisture_residual = 0.175
soil_moisture_saturation = 0.51
saturated_hydraulic_conductivity = 3.5e-05
van_genuchten_nonlinearily_parameter = 1.598
intercept_parameters = [
    0.935,
    0.498,
    0.00575,
]
veg_density_param = 0.046
groundwater_capacity = 500.0
bypass_flow_coefficient = 1.0
extinction_coefficient_global_radiation = 0.74
max_percolation_rate_uzlz = 2.7
groundwater_loss = 1.0
reservoir_const_upper_groundwater = 20.0
reservoir_const_lower_groundwater = 20.0
initial_aerodynamic_resistance_soil = 12.5
drag_coefficient_evaporation = 0.2
initial_stomatal_conductance = 1000.0
pore_connectivity_parameter = 0.5
air_entry_potential_inverse = 0.042
m_to_kpa = 9.804
hydrology.static

The model static mode setting. Default = False

hydrology.initial_soil_moisture

Initial soil moisture for all layers Default = 0.5

hydrology.initial_groundwater_saturation

Initial ground water saturation for all layers, unitless Default = 0.9

hydrology.p_wet_wet

Probability a wet day follows a wet day Default = 0.6

hydrology.p_wet_dry

Probability a wet day follows a dry day Default = 0.3

hydrology.rainfall_shape_parameter

Shape parameter of the Gamma distribution controlling rainfall variability Default = 1.5

hydrology.rainfall_scale_parameter

Scale parameter of the Gamma distribution controlling magnitude of rainfall Default = 1.0

hydrology.constants.soil_moisture_residual

Residual soil moisture, unitless.

The residual soil moisture refers to the water that remains in the soil after prolonged drainage due to the force of gravity. It is the water that is tightly held by soil particles and is not easily available for plant roots to extract. The value is soil specific, the format here is volumentic relative water content (unitless, between 0 and 1). Average value of different soil textures across tropical regions (Hodnett and Tomasella, 2002). Default = 0.175

hydrology.constants.soil_moisture_saturation

Soil moisture saturation, unitless.

Maximum amount of water a soil can hold when all its pores are completely filled with water — that is, the soil is fully saturated and contains no air in the pore spaces. Average value of different soil textures across tropical regions (Hodnett and Tomasella, 2002) . Default = 0.51

hydrology.constants.saturated_hydraulic_conductivity

Saturated hydraulic conductivity, [m s-1].

The saturated hydraulic conductivity is the measure of a soil’s ability to transmit water through its pores. More specifically, is defined as the volumetric flow rate of water passing through a unit cross-sectional area of soil under a unit hydraulic gradient (pressure difference). Value for average tropical rainforest taken from Gupta et al. (2022). Default = 3.5e-05

hydrology.constants.van_genuchten_nonlinearily_parameter

Nonlinearity parameter n (dimensionless) in Mualem-van Genuchten model.

This parameter is a fitting shape parameters of soil water retention curve, see (Van Genuchten, 1980). Average value of different soil textures across tropical regions is taken from Hodnett and Tomasella (2002). Default = 1.598

hydrology.constants.intercept_parameters

Interception parameters, unitless.

Parameters in equation that estimates maximum canopy interception capacity after Von Hoyningen-Huene (1981). Default = (0.935, 0.498, 0.00575)

hydrology.constants.veg_density_param

Parameter to estimate vegetation density for maximum interception, unitless.

This parameter is used to estimate the water holding capacity of a canopy after Von Hoyningen-Huene (1981). The value is taken from Van Der Knijff et al. (2010). Default = 0.046

hydrology.constants.groundwater_capacity

Ground water storage capacity, [mm].

This parameter indicates how much water can be stored in the ground water reservoir which affects the vertical flow of water and the horizontal sub-surface flow. This parameter is currently set to an arbitrary value; we are working on getting a best estimate. Default = 500

hydrology.constants.bypass_flow_coefficient

Empirical bypass flow coefficient, unitless.

This parameter affects how much of the water available for infiltration goes directly to groundwater via preferential bypass flow. A value of 0 means all surface water goes directly to groundwater, a value of 1 gives a linear relation between soil moisture and bypass flow. Default = 1.0

hydrology.constants.extinction_coefficient_global_radiation

Extinction coefficient for global radiation, [unitless].

This constant is used to reduce potential evaporation for bare soil to maximum shaded evaporation. Typical values are 0.4 to 0.7 for monocotyledons and 0.65 to 1.1 for broad leaved dicotyledons Monteith (1969). The value for tropical forest is taken from Saldarriaga and Luxmoore (1991). The extinction coefficient can be estimated from measurements of PAR above and below a canopy with a known LAI. Default = 0.74

hydrology.constants.max_percolation_rate_uzlz

Maximum percolation rate between upper and lower groundwater zone, [mm d-1].

Values for tropical rainforest are taken from van den Brink (2009). Default = 2.7

hydrology.constants.groundwater_loss

Constant ground water loss, [mm].

This parameter defines the constant amount of water that never rejoins the river channel and is lost beyond the catchment boundaries or to deep groundwater systems. Default = 1

hydrology.constants.reservoir_const_upper_groundwater

Reservoir constant for the upper groundwater layer, [days].

This parameter defines the residence time (in days) of water in the upper groundwater zone before contributing to streamflow, with typical values for tropical catchments ranging from 5 to 30 days depending on soil permeability and slope. This parameter is currently set to an arbitrary value; we are working on getting a better estimate. Default = 20

hydrology.constants.reservoir_const_lower_groundwater

Reservoir constant for the lower groundwater layer, [days].

This reservoir constant, measured in days, determines the residence time of water in the lower groundwater zone. It influences how quickly water exits the lower zone as baseflow. Typical values range from 10 to 5000 depending on catchment characteristics. This parameter is currently set to an arbitrary value; we are working on getting a better estimate. Default = 20

hydrology.constants.initial_aerodynamic_resistance_soil

Initial aerodynamic resistance at the soil surface, [s m-1].

This parameter is an initial estimate of the resistance to the transfer of momentum, heat, and water vapour between the soil surface and the atmosphere. The value is based on Australian evergreen forest, taken from Su et al. (2021); note that this assumes a dense canopy. Default = 12.5

hydrology.constants.drag_coefficient_evaporation

Drag coefficient for evaporation, dimensionless.

Represents the efficiency of turbulent transport of water vapour from a surface to the atmosphere. Default = 0.2

hydrology.constants.initial_stomatal_conductance

Initial stomatal conductance, [mmol m-2 s-1].

Initial estimate of the rate at which water vapor and carbon dioxide pass through the stomata of plant leaves, reflecting how open the stomata are and regulating both transpiration and gas exchange. Default = 1000.0

hydrology.constants.pore_connectivity_parameter

Pore connectivity parameter, dimensionless.

Dimensionless parameter used in van Genuchten-Mualem model to calculate unsaturated hydraulic conductivity. Default = 0.5

hydrology.constants.air_entry_potential_inverse

Inverse of air entry potential (parameter alpha in van Genuchten), [m-1].

The inverse of air entry potential describes how quickly soil water retention decreases with increasing soil suction, with higher values indicating coarser soils that drain more readily. Average value of different soil textures across tropical regions (Hodnett and Tomasella, 2002). Default = 0.042

hydrology.constants.m_to_kpa

Factor to convert matric potential from m to kPa. Default = 9.804