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Last update: May 2021

Biophysical Model

Community Land Model - CLM

In AGADAPT, the well developed and versatile Community Land Model (CLM) (version 4.0) was used to model the water and energy balance of a field site with Citrus trees. The Community Land Model, developed by the National Center for Atmospheric Research (NCAR) calculates soil moisture and evapotranspiration (Oleson et al., 2013). CLM uses the simplified Richards equation to model water flow in the unsaturated zone and for the calculation of the land surface fluxes the Monin-Obukhov similarity theory is invoked. The land cover is represented by 17 plant functional types (PFTs) and the calculation of surface fluxes is based on these PFTs. CLM derives soil hydraulic and thermal parameters on the basis of sand fraction, clay fraction and organic matter density. The following processes are simulated by CLM in the context of the AGADAPT project and real-time optimization of irrigation amounts: transfer of solar radiation and longwave radiation; momentum, sensible heat and latent heat fluxes; soil hydrology; stomatal physiology and photosynthesis; crop dynamics and irrigation (Oleson et al., 2013).

You can download the PDF Version here

Model description

CLM contains modules for the following land surface processes:

Vegetation composition, structure, and phenology
Absorption, reflection, and transmittance of solar radiation
Absorption and emission of longwave radiation
Momentum, sensible heat (ground and canopy), and latent heat (ground evaporation, canopy evaporation, transpiration) fluxes
Canopy hydrology (interception, throughfall, and drip)
Soil hydrology (surface runoff, infiltration, redistribution of water within the

column, sub-surface drainage, groundwater)

Stomatal physiology and photosynthesis

Figure 1. CLM components (http://www.cgd.ucar.edu/tss/clm)

Model inputs

Input Type	Variable identification and metric	Temporal scale	Data source
Atmospheric forcing	incident longwave (W/m²) incident solar (W/m²) precipitation (mm/s) pressure at the lowest level (Pa) relative humidity at the lowest level (%) temperature at the lowest level (K) wind at the lowest level (m/s)	hourly	ECMWF
Soil	sand fraction (%) clay fraction (%) organic matter density (Kg/m³)		Field
Vegetation	Vegetation type Root distribution parameters		CLM default
Leaf Area Index	The citrus leaf area index was calculated based on the ground coverage (fcover%) LAI = -1.3*Log(1-fcover%/100)/(1+fcover%/100)		Field

Model outputs

Output variable	Description	Units
FCTR	canopy transpiration	W/m²
FCEV	canopy evaporation	W/m²
FGEV	ground evaporation	W/m²
Qle	total evaporation	W/m²
QSOIL	ground evaporation	mm/s
QVEGE	canopy evaporation	mm/s
QVEGT	canopy transpiration	mm/s
QFLX_EVAP_TOT	qflx_evap_soi + qflx_evap_veg + qflx_tran_veg	mm H₂O/s
PET	Potential Evapotranspiration	mm H₂O/s
RAIN	atmospheric rain	mm/s
SNOW	atmospheric snow	mm/s
WT	total water storage (unsaturated soil water + groundwater)	Mm
H2OSOI	volumetric soil water	mm³/mm³
SOILLIQ	soil liquid water	kg/m²
QOVER	surface runoff	mm/s
QRUNOFF	total liquid runoff (does not include QSNWCPICE)	mm/s
QDRAI	sub-surface drainage	mm/s
SOILPSI	soil water potential in each soil layer	MPa

Condition of access to the model codes

Software is available to be used; CLM4.0 can be used freely (this was also checked with NCAR/UCAR), for the developed data assimilation routines a licensing condition will be followed.
Costs: to be agreed upon.
Contact: Prof. Dr. Harrie-Jan Hendricks-Franssen (h.hendricks-franssen@fz-juelich.de)

References:

Oleson, K., et al. (2013). "Technical Description of version 4.5 of the Community Land Model (CLM)." Ncar Technical Note NCAR/TN-503+STR, National Center for Atmospheric Research, Boulder, CO, 422 pp.