Biophysical Models

Published: 10/2/2017

Biophysical models simulate vegetation as the determinant in land surface interaction with the atmosphere. The simulated land/atmosphere exchange processes involve several budgetary calculations:

1. surface energy budget:

• calculate net surface radiation,
• including albedo and
• partitions between latent sensible and ground heat fluxes;

2. surface water balance:

• canopy transpiration,
• interception evaporation by canopy,
• ground evaporation,
• runoff,
• soil moisture,
• canopy water,
• and snow water equivalent;

3. The model also calculates:

• Carbon fluxes,
• air turbulence,
• stomatal resistance,
• and soil and air temperatures;

The model INPUTs include:

• Meteorological forcing
• Downward shortwave radiation [W/m2]
• Downward longwave radiation [W/m2]
• Surface air pressure [Pa]
• Precipitation rate [mm/sec]
• Air temperature [K] at the reference height
• Air moisture/humidity [kg/kg]
• Wind velocity at reference height [m/s]
• CO2 concentration [ppm]

The Simplified Simple Biosphere (SSiB) model [Xue et al., 1991, 1996 (SSiB-1), Sun and Xue, 2001 (SSiB-3), Zhan et al., 2003 (SSiB-2), Zhang et al, 2015 (SSiB-4)] was written in FORTRAN 77 and 90 languages to run on UNIX workstations and used GrADS to displaying the simulation results.

The land scheme simulates

• soil evaporation and vegetation evapotranspiration;
• runoff, soil moisture, and snow changes;
• Radiation, energy, and CO2 transfers and budgets;
• interactions between the vegetated land surface and the lower troposphere