soilwater module

Soil water movement and content module.

Model one-dimensional soil water movement (fluxes). Includes groundwater (assumes constant water table depth).

Author - Christopher Teh Boon Sung

SWC namedtuple

SWC(sat, fc, pwp, psd, porosity, airentry)

namedtuple: Soil water characteristics

sat

float: saturation point

fc

float: field capacity

pwp

float: permanent wilting point

psd

float: pore-size distribution

porosity

float: soil porosity

airentry

float: air-entry value

Texture namedtuple

Texture(clay, sand, om)

namedtuple: Soil texture

clay

float: percentage of clay

sand

float: percentage of sand

om

float: percentage of organic matter

AET namedtuple

AET(crop, soil)

namedtuple: Actual or reduction to evapotranspiration (ET)

crop

float: actual crop transpiration (or reduction of crop potential transpiration)

soil

float: actual soil evaporation (or reduction of soil potential evaporation)

RootWater class

Soil water characteristics in the rooting zone.

ATTRIBUTES

  • wc (float): water content (mm)
  • vwc (float): water content (m3/m3)
  • critical (float): critical water content, below which plant water stress occurs (m3/m3)
  • sat (float): saturation point (m3/m3)
  • fc (float): field capacity (m3/m3)
  • pwp (float): permanent wilting point (m3/m3)

Constructor __init__

RootWater(self)

Create and initialize the RootWater object.

SoilLayer class

Soil layer properties class.

The physical properties of a soil layer, dealing with soil water content and fluxes.

CLASS ATTRIBUTES

  • flux_fields (list): list of flux names (str) to serve as dictionary keys which are ['t', 'e', 'influx', 'outflux', 'netflux']

ATTRIBUTES

  • thick (float): Thickness of the soil layer (m)
  • texture: Sand, clay, and organic matter (%)
  • vwc (float): Vol. water content (m3/m3)
  • wc (float): Water content (mm)
  • accthick (float): Cumulative thickness (m)
  • depth (float): Depth of layer from soil surface (m)
  • swc (SWC): Soil water characteristics (varying units)
  • ksat (float): Saturated hydraulic conductivity (m/day)
  • k (float): Hydraulic conductivity (m/day)
  • matric (float): Matric head (m)
  • gravity (float): Gravity head (m)
  • fluxes (dict): Water flux components stored in a dictionary

The keys for the dictionary fluxes are as follows

    't': Plant water uptake via transpiration (m/day)
    'e':  Loss of water via evaporation (m/day)
    'influx': Water entry into layer (m/day)
    'outflux': Water exit out of layer (m/day)
    'netflux': Difference between influx and outflux (m/day)

METHODS

  • initialize_layer: Initialize all attributes
  • update_heads_k: Update the matric head, gravity head, and the unsaturated hydraulic conductivity
  • tothead: Total/sum of matric and gravity head (m) - getter method

Note

Volumetric water content (vwc) can be given as a negative value. Negative values are a special code to mean that the water content is a fraction between SAT and FC or between FC and PWP. The codes are along a scale from -3 to -1:

    Scale:
              -2.75      -2.25              -1.5
        [-3 ....|..........|....-2 ...........|..........-1]
         PWP                    FC                      SAT

so that if the given water content is -1, -2, or -3, it means the water content should be set to saturation, field capacity, or permanent wilting point, respectively. A value of -1.5 means the water content will be set at halfway between SAT and FC. Likewise, -2.25 and -2.75 mean the water content will be lower than FC, where the former (-2.25) means the water content will be set nearer to FC, but the latter (-2.75) closer to PWP.

Any negative values outside the range of -3 to -1 means the water content wil be set at FC.

Constructor __init__

SoilLayer(self)

Create and initialize the SoilLayer object.

initialize_layer

SoilLayer.initialize_layer(self, prevlayer, nextlayer)

Initialize all soil layer attributes.

Note

This function will set the water content to be within the range of SAT and FC or between FC and PWP, if the volumetric water content is given as negative value. See this class's docstring above.

Arguments

  • prevlayer (SoilLayer): previous soil layer (layer above current layer)
  • nextlayer (SoilLayer): next soil layer (layer beneath current layer)

Returns

None:

update_heads_k

SoilLayer.update_heads_k(self)

Update matric and gravity heads (m), and unsaturated hydraulic conductivity (m/day).

Update is based on current soil water content.

Returns

None:

tothead

Total head (m) - getter method.

Returns

float: total head

SoilWater class

Soil water balance class.

Model the soil water flow in one dimension and water balance. Include the effect of groundwater, if any, but assume constant water table depth.

EXTERNAL INFORMATION REQUIRED (MUST BE SUPPLIED FROM AN EXTERNAL CLASS)

    petcrop (float): Potential transpiration (from crop) (mm/day)
    petsoil (float): Potential evaporation (fro soil) (mm/day)

ATTRIBUTES

  • numintervals (int): Number of intervals for integration within a day
  • rootdepth (float): Rooting depth (m)
  • has_watertable (bool): True if water table / groundwater is present, else False
  • numlayers (int): Number of soil layers
  • layers (list): List of SoilLayer objects (their numbers must match numlayers)
  • rootwater (RootWater): Soil water characteristics in the root zone
  • cf (list): List of dictionary of cumulative fluxes for every soil layer
  • waterstresses (AET): Reduction to evaporation and transpiration due to water stress
  • netrain (float): Net rainfall (mm/day)
  • aet (AET): Actual water loss by evaporation and transpiration (mm/day)

METHODS

  • net_rainfall: Net rainfall (mm/day)
  • rooting_depth: Increase in rooting depth (m)
  • update_rootwater: Update the water content and water characteristics in the rooting zone
  • reduce_et: Reduction in evaporation and transpiration (0-1, 1=no stress, 0=max. stress)
  • actual_et: Actual evaporation and transpiration (mm/day)
  • influx_from_watertable: Influx of water from the water table (m/day).
  • calc_water_fluxes: Calculate the various water fluxes (m/day) for all soil layers
  • daily_water_balance: Solve for the water content in each soil layer
  • update: Update the soil water properties by solving the water fluxes

Constructor __init__

SoilWater(self, fname_in)

Create and initialize the SoilWater object.

Arguments

  • fname_in (str): path and filename of the model initialization file

net_rainfall

SoilWater.net_rainfall(self)

Net rainfall (mm/day).

Returns

float: net rainfall

rooting_depth

SoilWater.rooting_depth(self)

Increase in rooting depth (m).

Returns

float: rooting depth

update_rootwater

SoilWater.update_rootwater(self)

Update the water content and water characteristics in the rooting zone.

The RootZone object will be set here.

Note

Critical soil water content for plant water stress taken as 0.6 or 60% of the difference between soil saturation and permanent wilting point.

Returns

None:

reduce_et

Reduction in evaporation and transpiration (0-1, 1=no stress, 0=max. stress).

Returns

AET: namedtuple containing reduction in E and T (float)

actual_et

Actual evaporation and transpiration (mm/day).

Arguments

  • petcrop (float): potential water loss from the crop (mm/day)
  • petsoil (float): potential water loss from the soil (mm/day)

Returns

AET: namedtuple containing actual water loss from soil and crop (float)

influx_from_watertable

SoilWater.influx_from_watertable(self)

Influx of water from the water table (m/day).

Returns

float: groundwater influx

calc_water_fluxes

SoilWater.calc_water_fluxes(self, petcrop, petsoil, firstrun)

Calculate the various water fluxes (m/day) for all soil layers.

Flux can either have a positive or negative sign

    +ve flux - means downward flow
    -ve flux - means upward flow (against gravity)

Arguments

  • petcrop (float): potential water loss from the crop (mm/day)
  • petsoil (float): potential water loss from the soil (mm/day)
  • firstrun (bool): set to True for first run, else False. True means the cumulative fluxes will be initialize with the first set of flux values. False will accumulate the flux values.

Returns

None:

daily_water_balance

SoilWater.daily_water_balance(self, petcrop, petsoil)

Solve for the water content in each soil layer.

Arguments

  • petcrop (float): potential water loss from the crop (mm/day)
  • petsoil (float): potential water loss from the soil (mm/day)

Returns

None:

update

SoilWater.update(self, external_info)

Update the soil water properties by solving the water fluxes.

Arguments

  • external_info (dict): requires information on potential transpiration and evaporation

Returns

None: