Module Vegetation

Overview

Vegetation Model handles information about vegetation cover and interacts with atmosphere and soil properties. Vegetation dynamics can be handled by the model in two different manners: i) reading from file (time serie, hdf, grid); ii) using a vegetation growth model. The first option is the previous formulation where LAI and root depth properties are provided by user and water uptake is simulated. The second option uses a SWAT based vegetation growth model and plant biomass, LAI, nutrient content and nutrient uptake are explicitly simulated.

SWAT vegetation growth model uses the concepts from EPIC crop model (Izaurralde et al., 2006) of radiation-use efficiency by which a fraction of daily photosynthetically active radiation is intercepted by the plant canopy and converted into plant biomass. Gains in plant biomass are affected by vapor pressure deficits and atmospheric CO2 concentration. Stress indices for water, temperature, nitrogen, phosphorus and aeration are calculated using the value of the most severe of these stresses to reduce potential plant growth and crop yield. Nutrient uptake is done based on plant target (optimal content) and availability in soil.

Concepts

Property

Vegetation model was redesigned to be structured in properties instead of vegetation types. The advantage of this structure is that in the input file the number of properties is fixed (no matter the complexity of the vegetation cover) and input can be preprocessed for the entire grid (see How to pre-process vegetation). In the previous structure, applications with several vegetation covers could rapidly increase input file lines and input errors. More over as they are not graphed in time serie or hdf the visual inspection could take longer.

See the list of allowed properties names

How to Pre-Process Vegetation

Fill Matrix was updated to fill grids without interpolation. Instead of space stations (X,Y coordinate) user has to provide a vegetation grid with ID's and the values assigned to each ID (time serie or single value). Fill Matrix reads ID in the grid and searches for the value to fill the cell. If cells are not filled error message is sent. See FillMatrix for more details

Outputs

Time series

To write time series results define keyword:

TIME_SERIE           : 1

in each property that you wish to write results.

Maps (HDF5 format)

To write 3D results use keyword OUTPUT_TIME and define keyword:

OUTPUT_HDF           : 1

in each property that you wish to write results.

References

Izaurralde, R.C.; Williams, J.R. ; McGill, W.B.; Rosenberg, N.J.; Quiroga Jakas, M.C. (2006) - Simulating soil C dynamics with EPIC: Model description and testing against long‐term data. Ecol. Model. 192(3‐4): 362‐384.

Other

Some keywords/properties od the input file vegetation_x.dat are:

<beginvegetationtype>

ID                        : 1
NAME                      : Sample vegetation type

<<begin_property>>
!total leaf are / projected crown area
PROPERTY_NAME             : leaf area index
IS_CONSTANT               : 1
CONSTANT_VALUE            : 0
<<end_property>>

<<begin_property>>
!the depth of water that can be retained by leaves of a particular species per unit leaf area
PROPERTY_NAME             : specific leaf storage
IS_CONSTANT               : 1
CONSTANT_VALUE            : 0
<<end_property>>

<<begin_property>>
!factor for lowering evapotranspiration due to the crop type based on a reference evapotranspiration 
PROPERTY_NAME             : evtp crop coefficient
IS_CONSTANT               : 1
CONSTANT_VALUE            : 1
<<end_property>>

<<begin_property>>
!self declaring...
PROPERTY_NAME             : root depth
IS_CONSTANT               : 1
CONSTANT_VALUE            : 0
<<end_property>>

<<begin_property>>
!Parameter of the root water uptake model after FEDDES (1978): 'Simulation of field water use and crop yield'
PROPERTY_NAME             : feddes h1
IS_CONSTANT               : 1
CONSTANT_VALUE            : -0.1
<<end_property>>

<<begin_property>>
!Parameter of the root water uptake model after FEDDES (1978): 'Simulation of field water use and crop yield'
PROPERTY_NAME             : feddes h2
IS_CONSTANT               : 1
CONSTANT_VALUE            : -0.25
<<end_property>>

<<begin_property>>
!Parameter of the root water uptake model after FEDDES (1978): 'Simulation of field water use and crop yield'
PROPERTY_NAME             : feddes h3
IS_CONSTANT               : 1
CONSTANT_VALUE            : -5.0
<<end_property>>

<<begin_property>>
!Parameter of the root water uptake model after FEDDES (1978): 'Simulation of field water use and crop yield'
!Wilting point
PROPERTY_NAME             : feddes h4
IS_CONSTANT               : 1
CONSTANT_VALUE            : -80.0
<<end_property>>

<<begin_property>>
!self declaring...
PROPERTY_NAME             : permeable fraction
IS_CONSTANT               : 1
CONSTANT_VALUE            : 1.0
<<end_property>>

<endvegetationtype>