Module Basin

Overview

Module Basin is a connection among the different modules of Mohid-Land. Indeed it manages the entering data, namely the water column, that is updated after each call of each module. The final results of this module is the different water fluxes due to evapotranspiration, runoff and infiltration.

Main Processes

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

• Reading entering data and grid construction
• Atmospheric processes in order to obtain the water column from the precipitation
• Call of Module PorousMedia in order to obtain the infiltration rate
• Update of the water column
• Call of Module Runoff
• Redistribution of the fluxes into the water body
• Output of the different components of the water flux

Evapotranspiration

Some water may disappear from the soil because of the evaporation and transpiration processes, which become a sink in soil water profile. These two processes, currently named 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)

Potential evapotranspiration is calcuçtaed made in module Basin. However, not all of the potential water that can be evaporated or transpirated will be in fact removed from the soil. The water that will really leave the soil through these processes is calculated in the Module PorousMedia.