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Soil Moisture Parameters

This section documents the parameters in MONICA's general/soil-moisture.json file. They control infiltration, percolation, groundwater discharge, soil evaporation, precipitation partitioning, and snowpack processes.

List of soil moisture parameters

Parameter Name Type Unit Description Example
CorrectionRain Number Multiplier applied to the liquid fraction of net precipitation after rain–snow partitioning "CorrectionRain": 1
CorrectionSnow Number Multiplier applied to the solid fraction of net precipitation after rain–snow partitioning "CorrectionSnow": 1.14
CriticalMoistureDepth Number m Legacy parameter retained in the standard parameter file. It is not read or used by the current MONICA core. "CriticalMoistureDepth": 0.3
EvaporationZeta Number Shape factor used to distribute potential soil evaporation over the evaporation-affected soil layers. The implementation expects a value approximately in the range 0–40. "EvaporationZeta": 40
GroundwaterDischarge Number mm d-1 Prescribed water flux used for drainage in soil layers influenced by groundwater "GroundwaterDischarge": 3
HydraulicConductivityRedux Number Multiplier applied to saturated hydraulic conductivity when calculating infiltration. The frost module may modify the effective multiplier according to soil frost and thaw conditions. "HydraulicConductivityRedux": 0.1
KcFactor Number Fallback crop coefficient used to calculate potential evapotranspiration as ET₀ × Kc when no crop is growing. When a crop is present, the crop module supplies its own Kc value. "KcFactor": 0.75
MaxPercolationRate Number mm d-1 Maximum downward percolation rate allowed for a soil layer during one daily timestep "MaxPercolationRate": 10
MaximumEvaporationImpactDepth Number dm Maximum nominal depth over which potential soil evaporation is distributed. The implementation also uses this value when determining the affected layer indices. "MaximumEvaporationImpactDepth": 5
MoistureInitValue Number m3 m-3 Legacy/reserved initial-moisture parameter. It is read and serialized but is not currently used to initialize soil moisture in the MONICA core. "MoistureInitValue": 0
NewSnowDensityMin Number kg dm-3 Minimum density of newly fallen snow "NewSnowDensityMin": 0.1
RefreezeParameter1 Number Coefficient controlling the amount of liquid water that refreezes in the snowpack below RefreezeTemperature "RefreezeParameter1": 1.5
RefreezeParameter2 Number Exponent applied to the temperature difference in the snow-refreezing equation "RefreezeParameter2": 0.36
RefreezeTemperature Number °C Temperature threshold below which liquid water in the snowpack may refreeze "RefreezeTemperature": -1.7
SaturatedHydraulicConductivity Number mm d-1 Saturated hydraulic conductivity used by the infiltration calculation. The configured value is applied uniformly to the soil-moisture layers. "SaturatedHydraulicConductivity": 8640
SnowAccumulationTresholdTemperature Number °C Upper temperature threshold for precipitation partitioning. At or above this temperature, precipitation is entirely liquid. Between this value and TemperatureLimitForLiquidWater, precipitation is divided between rain and snow. "SnowAccumulationTresholdTemperature": 1.8
SnowMaxAdditionalDensity Number kg dm-3 Maximum density increment above NewSnowDensityMin. Together, the two parameters define the maximum modeled snow density. "SnowMaxAdditionalDensity": 0.25
SnowMeltTemperature Number °C Base temperature above which snowmelt can occur "SnowMeltTemperature": 0.31
SnowPacking Number Fractional increase used when calculating daily compaction of the existing snowpack "SnowPacking": 0.01
SnowRetentionCapacityMax Number kg kg-1 Maximum fraction of snow water equivalent that the snowpack can retain as liquid water. Liquid water above the retention capacity is released from the snowpack. "SnowRetentionCapacityMax": 0.17
SnowRetentionCapacityMin Number kg kg-1 Minimum fraction of snow water equivalent that the snowpack can retain as liquid water "SnowRetentionCapacityMin": 0.05
SurfaceRoughness Number m Average amplitude of surface micro-elevations. It affects temporary surface-water storage and surface-runoff calculations. "SurfaceRoughness": 0.02
TemperatureLimitForLiquidWater Number °C Lower temperature threshold for precipitation partitioning. At or below this temperature, incoming precipitation is entirely snow. "TemperatureLimitForLiquidWater": -3
XSACriticalSoilMoisture Number Calibration factor used by the THESEUS soil-evaporation reduction method when calculating critical soil moisture under crop cover "XSACriticalSoilMoisture": 0.1
type String Declares that this JSON defines soil moisture parameters "type": "UserSoilMoistureParameters"

Note

All parameters apply globally to the soil profile unless otherwise specified. These values are typically set in the general/soilmoisture.json file within the monica-parameters repository.

Rain and snow partitioning

MONICA divides net precipitation into liquid and soil fractions using two temperature thresholds:

  1. At or above SnowAccumulationTresholdTemperature, all precipitation is treated as rain.
  2. At or below TemperatureLimitForLiquidWater, all precipitation is treated as snow.
  3. Between the two thresholds, precipitation is divided linearly between rain and snow.

The resulting liquid and solid fractions are multiplied by CorrectionRain and CorrectionSnow, respectively.

Example: soil-moisture.json

{
    "CorrectionRain": 1,
    "CorrectionSnow": 1.14,
    "CriticalMoistureDepth": 0.3,
    "EvaporationZeta": 40,
    "GroundwaterDischarge": 3,
    "HydraulicConductivityRedux": 0.1,
    "KcFactor": 0.75,
    "MaxPercolationRate": 10,
    "MaximumEvaporationImpactDepth": 5,
    "MoistureInitValue": 0,
    "NewSnowDensityMin": 0.1,
    "RefreezeParameter1": 1.5,
    "RefreezeParameter2": 0.36,
    "RefreezeTemperature": -1.7,
    "SaturatedHydraulicConductivity": 8640,
    "SnowAccumulationTresholdTemperature": 1.8,
    "SnowMaxAdditionalDensity": 0.25,
    "SnowMeltTemperature": 0.31,
    "SnowPacking": 0.01,
    "SnowRetentionCapacityMax": 0.17,
    "SnowRetentionCapacityMin": 0.05,
    "SurfaceRoughness": 0.02,
    "TemperatureLimitForLiquidWater": -3,
    "XSACriticalSoilMoisture": 0.1,
    "type": "UserSoilMoistureParameters"
}