Chapter 5 ....continued
Dynamic Water Balance Modelling

Section 5.8

5.8

Vegetation data inputs
The evapotranspiration, plant growth and sediment transport modules require data for each vegetation type represented in the catchment. Most of this information is stored in the .veg file, though a few parameter values are stored in the .par file (see section 5.13) and some ancillary files.

Two different types of .veg file are used, depending on which modules are invoked in Topog_dynamic. A type 1 .veg file is used when the plant growth option is not invoked. This file type is also used when the sediment transport option is invoked. A type 2 .veg file is used only when the plant growth option is invoked.

If the model is run on a sub-daily timestep, without sediment transport, then a .veg file is not needed, as evapotranspiration is not computed.

5.8.1 Contents of the .veg file when the plant growth option is not invoked

When the plant growth option is not invoked, the vegetation data input requirements are quite simple. For such a case, an example type 1 .veg file with two vegetation types (eucalypt trees and perennial grass) might look like this:

# Acan Asoil Rint Lex ccmax m lwpmax rmax
ra rs rootfn rootwt fmgu canopa canoph
0.10 0.15 0.0005 -0.42 0.003 0.04 -150 10.0
20.0 100.0 0 1 0.1 0.9 7.5
0.10 0.15 0.0003 -0.65 0.0025 0.03 -200 1.5
50.0 70.0 1 1 0.4 0.7 0.2

where the parameters (from left to right) are:

Variable Units Typical values Description
Acan (0-1) 0.1 - 0.3 albedo of the canopy; ignore if running model on a sub-daily timestep
Asoil (0-1) 0.1 - 0.35 albedo of the soil; ignore if running model on a sub-daily timestep
Rint m/lai/d 0.0003 - 0.0007 canopy interception coefficient; ignore if running model on a sub-daily timestep
Lex (0-1) 0.3 - 0.6 canopy light extinction coefficient; ignore if running model on a sub-daily timestep
iccmax m/s 0.001 - 0.006 maximum canopy conductance; ignore if running model on a sub-daily timestep
m . 0.002 - 0.2 slope of the line relating vapour pressure deficit to canopy conductance; ignore if running model on a sub-daily timestep
lwpmax m -80 - -200 maximum plant available soil water potential; ignore if running model on a sub-daily timestep
rmax m 0.2 - 40.0 maximum plant rooting depth; ignore if running model on a sub-daily timestep
ra s/m 15 - 60 aerodynamic resistance for the plant canopy; ignore if running model on a sub-daily timestep
rs s/m 50 - 110 aerodynamic resistance for the soil surface; ignore if running model on a sub-daily timestep
rootfn integer 0, 1 or 2 rooting density function flag (see below) ; ignore if running model on a sub-daily timestep
xrootwt (0-1) 0-1 ignore this item; set to 1 for now
C1
or
fmgu 		(0-1) 0-1 fraction of exposed soil, where 1 denotes soil is completely exposed and 0 denotes soil is completely covered; only needed when sediment transport option is invoked; see eq. 5.23
c
or
canopa 		(0-1) 0-1 fraction of canopy cover, where 1 denotes full canopy cover and 0 denotes no canopy cover; only needed when sediment transport option is invoked; see eq. 5.24
H
or
canoph 		m 0 - 30 distance from ground to gravity centre of plant canopy; only needed when sediment transport option is invoked; see eq. 5.26

For each vegetation type, the user may select from three rooting density functions. These are:

Flag Description of rooting density function
0 Ritchie exponential decay with depth. This decay function is bounded by the minimum of either the specified maximum rooting depth (rmax) or the depth of the soil profile.
1 Proportionate extraction from each soil profile compartment based on compartment thickness.
2 Power-law extraction of the form x * (thickness)m where the constant x and exponent m are specified at the end of the vegetation file.

If only one line of data is provided in the .veg file, then Topog_dynamic assumes that a single vegetation type is used for the catchment, and that there is only one vegetation layer. If more than one line of data is included in the .veg file then this implies that multiple vegetation types or layers are being specified.

If multiple vegetation types are nominated, an overlay file defining the distribution of these types within the catchment must also be specified (see section 5.12.1). An overlay file is not needed if there is one type of overstorey and one type of understorey distributed uniformly across the catchment (in this case, two lines of data would be needed in the .veg file).

5.8.2 Additional vegetation inputs when the plant growth option is not invoked

For each vegetation type represented in the catchment, a leaf area index (LAI) value must be given. This can be a single value for each vegetation layer, or a spatial map of values for the catchment (see section 5.12.3), generated using Topog_overlay. In both cases, the LAI value or filename of LAI values must be specified in the .par file, built using Topog_simgen (see section 5.13).

5.8.3 Contents of the .veg file when the plant growth option is invoked

When the plant growth option is invoked, the vegetation data input requirements are more complicated. For such a case, an example type 2 .veg file with four vegetation types (each line is a different type) might look like this.

#Acan Asoil Rint Lex Amax g1 lwpmax WH
WN Thalf Topt jdgerm ddh Qpsat rmax sla
xleafres xstemres xrootres xlmort xsmort xrmort abpart saltf
ra rs xrootwt type
0.10 0.15 0.002 -0.42 0.012 0.3 -150 0.2
0.2 10 25 -1 -1 1200. 6.0 12.0
0.0004 0.0003 0.0004 0.001 0.0001 0.001 0.2 1.0
20.0 110.0 1. #eucalypt trees
0.10 0.15 0.0007 -0.65 0.010 0.7 -200 0.2
0.5 10 20 -1 -1 1000. 2.0 24.0
0.002 -1 0.0002 0.001 -1 0.001 0.1 1.0
50.0 60.0 1. # perennial pasture
0.10 0.15 0.0003 -0.65 0.025 0.7 -150 0.2
0.5 5 25 153 15000 1000. 1.5 24.0
0.004 -1 0.0012 0.004 -1 0.004 0.4 1.0
30.0 90.0 1. #wheat
0.10 0.15 0.0007 -0.65 0.024 0.7 -150 0.2
0.5 10 25 -1 -1 1200. 3.0 24.0
0.002 -1 0.002 0.001 -1 0.001 0.3 1.0
30.0 90.0 1. #lucerne

where the parameters (from left to right) are:

Variable Units Typical values Description
Acan (0-1) 0.1 - 0.3 albedo of the canopy
Asoil (0-1) 0.1 - 0.3 albedo of the soil
Rint m/lai/d 0.0001 - 0.002 canopy interception coefficient
Lex . -0.3 - -1.0 canopy light extinction coefficient
Amax kg C/m2 leaf 0.01 - 0.03 maximum carbon assimilation rate; see eq. 5.12 and eq. 5.17
g1 . 0.1 - 1 stomatal control coefficient; related to the vpd dependence; see eq. 5.11
lwpmax m -80 - -200 maximum plant available soil water potential
WH (0-1) 0.2/0.8 ratio of mesophyll to stomatal conductance; use 0.2 for C3 plants (eg. wheat, eucalypts, pines) and 0.8 for C4 plants (eg. sedges); see eq. 5.16
WN (0-1) 0-1 nutrient weighting parameter; a value of 1 means that nutrients are limiting, a value of 1 means that nutrient content limits growth as much as water content, a value of 0 means that nutrients do not limit growth; see eq. 5.16
Thalf oC 10-20 temperature half saturation rate; see eq. 5.16
Topt oC 20-30 optimal temperature for assimilation; see eq. 5.16
jdgerm day number 1 - 365 germination day number for annuals; use value of -1 if annuals not used
ddh days oC 10000 - 20000 degree day hours to senescence value; use value of -1 if annuals not used
Qpast mmoles/m2 leaf /s1 1200 - 1800 light saturation intensity; see eq. 5.16
rmax m 0.2 - 40.0 maximum plant rooting depth
sla m2 leaf /kg leaf C 10-60 leaf area per unit mass of leaf carbon
xleafres kg/kg/d 0.001 - 0.004 leaf maintenance respiration coefficient
xstemres kg/kg/d 0.0001 - 0.0004 stem maintenance respiration coefficient; set to -1 for non-woody plants
xrootres kg/kg/d 0.001 - 0.004 root maintenance respiration coefficient
xlmort kg/kg/d 0.01 - 0.03 daily leaf mortality rate
xsmort kg/kg/d 0.01 - 0.03 daily stem mortality rate; set to -1 for non-woody plants
xrmort kg/kg/d 0.01 - 0.03 daily root mortality rate
abpart (0-1) 0.2 - 0.6 proportion of total fixed carbon allocated to stem and leaf
saltf . 0 - 4 salt sensitivity parameter; a value of 1 means that salt content limits growth as much as water content, a value of 0 means that salt does not limit growth; this is usually set to 1
ra s/m 15 - 60 aerodynamic resistance for the plant canopy
rs s/m 50-110 aerodynamic resistance for the soil surface
xrootwt (0-1) 0-1 ignore this item; set to 1 for now
type text . vegetation type; enter any text string as a descriptor, starting with '#'

5.8.4 Additional vegetation inputs when the plant growth option is invoked

For each vegetation type represented in the catchment, the following information must be provided:

The .rootc file contains a single column of values (in units of kg/m2) and must have the same number of lines as the .nodes file it is linked to (see section 5.7.1). Unlike soil water solute concentration, the root carbon value is a total mass for the block of soil centred on each node. For this reason, zero values are ascribed to the top and bottom nodes.

.nodes file .rootc file 
 0.0	1 	0.005
 0.001	1	0.004
 0.05	1	0.003
 0.1	1	0.003
 0.3	1	0.003
 0.5	2	0.002
 0.7	2	0.002
 1.0	2	0.002 
 0.0
 0.01
 0.02
 0.02
 0.03
 0.02
 0.02
 0.0

The .rootc file is ignored if a simulation is started with a .fin file.

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last modified on 24 June 1997