BAITSSS Features
Approach
BAITSSS establishes radiative, convective, and conductive components of the surface energy balance for soil and canopy surfaces.
BAITSSS assumes vertical transfer of fluxes, vapor pressure, and water without lateral interactions between the cells.
BAITSSS integrates fluxes from soil and canopy using fraction of vegetation cover (fc ) based on vegetation indices.
BAITSSS utilizes standard and complete surface energy balance with fundamental aerodynamic equations of latent heat flux (LE) and sensible heat flux (H).
BAITSSS adopts resistance formulations from Jarvis, 1976; Sun, 1982; Shuttleworth and Wallace, 1985; Choudhury and Monteith, 1988.
BAITSSS iteratively solves surface energy balance components with Monin-Obukhov stability parameters for each time step to calculate surface temperature at soil surface (Ts) and canopy level (Tc) (Dhungel et al., 2016; Dhungel et al., 2016a).
The variables of surface energy balance inside the nested loop were backward averaged to accelerate the iteration process and avoid non-convergence.
The temperature at the intermediate height i.e. d + zom is not determined in BAITSSS to eliminate one of the uncertain variables, so the overall model structure can be reasonably compared to a parallel model.
BAITSSS estimates ground heat flux (G) based on sensible heat flux (Hs) and net radiation (Rn_s) of soil surface and assume no G on vegetated surface.
BAITSSS adopts canopy resistance (rsc) formulation from the Jarvis-type model with weighing functions representing plant response to solar radiation (F1), air temperature (F2), vapor pressure deficit (F3), and soil moisture at the root zone (F4) ) (Alfieri and Niyogi, 2008; Kumar et al., 2011), each varying between 0 (infinite resistance) to 1 (no resistance).
The canopy resistance (rsc) is a function of a wide range of environmental variables along with soil moisture at the root-zone and a constant minimum canopy resistance (Rc_min) which dynamically controls the transpiration process.
BAITSSS computes soil surface resistance (rss) based on saturated soil moisture (θsat) and soil surface moisture content (θsur) (Sun, 1982).
BAITSSS implements a basic but fundamental two-layered soil water balance model, i.e., soil surface (dsur ~ 100 mm depth) and root zone (droot ~ 500 mm - 2000 mm depth) to track soil evaporation (Ess) and transpiration (T) separately.
BAITSSS restricts soil surface and root zone moisture to field capacity (θfc ), i.e., water above field capacity either become run-off or deep percolated below the root zone.
BAITSSS simulates irrigation (Irr) in agricultural landscape based on irrigation type (i.e., sprinkler, drip etc.) using Management Allowed Depletion (MAD) and threshold moisture at root zone (θt) .
Instantaneous latent heat flux (LE) (W m-2 ) is converted to equivalent water (mm of ET) by latent heat of vaporization (λ) for each time step.
Generally, there is closure of the surface energy budget in the daytime within ten iterations unless there is a difficulty in convergence in extremely low wind speed.