Module Basin

Overview

Module Basin works as an interface among the different modules of Mohid-Land. Indeed it manages fluxes between modules as precipitation, evapotranspiration, infiltration, etc and updates water column and concentration after each module call. This module is able to compute a water and mass balance for each property transported in all mediums.

Main Processes

The processes made in the Module Basin can be summarized as following:

• Reading entering data and grid construction
• Atmospheric processes (precipitation, leaf interception, leaf drainage, evaporation) in order to obtain the potential water column
• Call of Module PorousMedia giving potential water column and obtain the infiltration rate
• Update of the water column and send it to ModuleRunoff (the holder of water column)
• Call of Module PorousMediaProperties and update of water column concentrations send it to the ModuleRunoffProperties
• Call of Module Runoff giving the remaining water columns to be transported
• Call of Module RunoffProperties

(When Module Runoff and RunoffProperties run as they are the holders of water column and water column concentration, no update is needed).

• Call of Module DrainageNetwork to route the water in the river and the new transfered from groundwater and from runoff.
• Output of the different components of the water and property flux

Evapotranspiration

Some water may be extracted from the soil because of the evaporation and transpiration processes, which become a sink in soil water profile. These two processes are currently named Evapotranspiration and Potential Evapotranspiration may be modeled using the Penmann Monteith equation:

$\overset{\text{Energy flux rate}}{\lambda_v E=\frac{\Delta R_n + \rho_a c_p \left( \delta q \right) g_a }{\Delta + \gamma \left ( 1 + g_a / g_s \right)}}~ \iff ~ \overset{\text{Volume flux rate}}{ET_o=\frac{\Delta R_n + \rho_a c_p \left( \delta q \right) g_a } { \left( \Delta + \gamma \left ( 1 + g_a / g_s \right) \right) \lambda_v }}$

λ_v = Latent heat of vaporization. Energy required per unit mass of water vaporized. (J/g)

L_v = Volumetric latent heat of vaporization. Energy required per water volume vaporized. (L_v = 2453 MJ m^-3)

E = Mass water evapotranspiration rate (g s^-1 m^-2)

ET_o = Water volume evapotranspired (m³ s^-1 m^-2)

Δ = Rate of change of saturation specific humidity with air temperature. (Pa K^-1)

R_n = Net irradiance (W m^-2), the external source of energy flux

c_p = Specific heat capacity of air (J kg^-1 K^-1)

ρ_a = dry air density (kg m^-3)

δe = vapor pressure deficit, or specific humidity (Pa)

g_a = Hydraulic conductivity of air, atmospheric conductance (m s^-1)

g_s = Conductivity of stoma, surface conductance (m s^-1)

γ = Psychrometric constant (γ ≈ 66 Pa K^-1)

The Penman Montheith Potential Evapotranspiration computation will be active if in basin file

EVAPOTRANSPIRATION : 1

and the property evapotranspiration is not readed from file.

if the user is running with vegetation

than Crop Evapotranspiration is obtained from Potential Evapotranspiration using crop coefficient from Module Vegetation (dependent on crop).

$CropEvapoTransp = PotentialEvapoTransp * CropCoefficient$

Also if the user is running with vegetation a differentiation in Crop Evapotranspiration between Potential Transpiration and Potential Evaporation may be done using LAI:

EVAPOTRANSPIRATION_METHOD : 2

$PotentialTrans = CropEvapoTransp * (1 - e^{-0.463 * LAI})$

$PotentialEvap = CropEvapoTransp - PotentialTrans$

if the user is running with vegetation and does not want the Crop Evapotranspiration to be separated in Potential Transpiration and Potential Evaporation then

EVAPOTRANSPIRATION_METHOD : 1

there will not be evaporation in Module PorousMedia and Crop Evapotranspiration is all transpiration (in Module Vegetation).

if the user is not running with vegetation

than Potential Evapotranspiration is all evaporation in the soil surface and will be done in Module PorousMedia.

The Potential transpiration computed in Module Basin is given to Module Vegetation to compute the effective transpiration. Potential Evaporation computed in Module Basin is given to Module Porous Media to compute the effective evaporation.

Data File

Keywords

ATMOSPHERE                    : 0/1              [1]          !Use Module Atmosphere 
POROUS_MEDIA                  : 0/1              [1]          !Use Module Porous Media
POROUS_MEDIA_PROPERTIES       : 0/1              [1]          !Use Module Porous Media Properties
RUN_OFF                       : 0/1              [1]          !Use Module RunOff
RUN_OFF_PROPERTIES            : 0/1              [1]          !Use Module RunOff Properties
DRAINAGE_NET                  : 0/1              [1]          !Use Module Drainage Netork
DT_DURING_RAIN                : sec.             [60.]        !initial dt that is tried when rains in the time step
EVAPOTRANSPIRATION_METHOD     : integer          [1]          !1- evapotranspiration - everything in crops; 2- separate
                                                              !between evaporation (surface soil) and transpiration (in crops)
EVAP_FROM_CANOPY              : 0/1              [1]          !Evaporate from plant leafs
EVAP_FROM_WATER_COLUMN        : 0/1              [0]          !Evaporate from water column.
OUTPUT_TIME                   : sec. sec. sec.    -           !Output Time
TIME_SERIE_LOCATION           : char              -           !Path to time serie location file

Computed or user defined potential evapotranspiration
<beginproperty>
NAME                      : reference evapotranspiration
UNITS                     : mm/h
DESCRIPTION               : fao evapotranspiration
DEFAULTVALUE              : 0.0
REMAIN_CONSTANT           : 0
<endproperty>

Sample

ATMOSPHERE                : 1
EVAPOTRANSPIRATION        : 1
EVAPOTRANSPIRATION_METHOD : 1
VEGETATION                : 0
POROUS_MEDIA              : 1
POROUS_MEDIA_PROPERTIES   : 1
RUN_OFF                   : 1
RUN_OFF_PROPERTIES        : 1
DRAINAGE_NET              : 0

!OUTPUT_TIME              : 0 7200
TIME_SERIE_LOCATION       : ..\General Data\TimeSeries\TimeSeriesLocation2D_2.dat
VERIFY_MASS               : 1
CONTINUOUS                : 0
DT_DURING_RAIN            : 3600. 
 
EVAP_FROM_CANOPY          : 1
EVAP_FROM_WATER_COLUMN    : 0

<beginproperty>
NAME                      : reference evapotranspiration
UNITS                     : mm/h
DESCRIPTION               : fao evapotranspiration
DEFAULTVALUE              : 0.0
REMAIN_CONSTANT           : 0
<endproperty>