Chapter 5 ....continued
Dynamic Water Balance Modelling

Sections 5.3 to 5.5

5.3

Overview of inputs to Topog_dynamic
The data inputs to Topog_dynamic can be summarised under ten main headings:

Before we describe the specific inputs needed for the model, it is worth reviewing the combinations of modules which can be invoked in a Topog_dynamic run.

. Model option Compatible with options
1 plant growth simulated 2,4,7,8
2 solute transport simulated 1,4,7,8
3 sediment transport simulated 5,6,7,9
4 evapotranspiration simulated 1,2,6,7,8
5 kinematic wave overland flow simulated 3,6,7,9
6 soil water accounting by Simplified Bucket Model 3,4,5,8,9
7 soil water accounting by Richards equation 1,2,3,4,5,8,9
8 daily time step used 1,2,3,6,7
9 sub-daily timestep used 3,5,6,7

Hence, the specific data input requirements for a Topog_dynamic run vary, according to what combinations of processes are simulated and in what manner. For example, the vegetation files needed for running the model with and without the plant growth option invoked are quite different. Similarly, different climate files are needed to run the model on a daily and sub-daily basis.

In the following sections, we specify the exact data input requirements under each of the seven headings above.

5.4

Topographic data inputs
The topographic data inputs are the same as for Topog_simul, and do not vary amongst different run modes in Topog_dynamic.

Either Topog_element or Topog_stripgen must be used to build the following files:

5.5

Climate data inputs

5.5.1 Different types of .climate files

Climatic inputs vary depending on whether the model is run in daily or sub-daily timestep mode. In both cases, a non-mandatory filename extension of .climate is used but we refer to the different files as type 1 and type 2 files.

A type 1 .climate file (used for daily timestep simulations) contains the following data items:

  • day number (indexed to 1/1/reference year)
  • daily maximum temperature (oC)
  • daily minimum temperature (oC)
  • mean daily vapour pressure deficit (mbars)
  • total daily rainfall (mm/day)
  • total solar radiation on the horizontal (KJ/m2/day)

Here are the first few lines of a typical type 1 .climate file: 

&HEADER
&  1 10 &Day
& 11 10 &Maximum Temperature
& 21 10 &Minimum Temperature
& 31 10 &Vapour Pressure Deficit
& 41 10 &Rainfall
& 51 10 &Total Solar Radiation
&END HEADER
#Date - 01011992
	1	22.00	16.60	2.96	27.3000	2486.75
	2	25.40	12.00	8.61	.0000	24380.12
	3	21.80	16.20	5.22	1.5000	12752.32

A type 2 .climate file (used for sub-daily timestep simulations) contains the following data items:

  • time in fractions of a day (indexed to 1/1/reference year)
  • instantaneous rainfall (mm/time step)

Here are the first few lines of a typical type 2 .climate file: 

&HEADER
&  1 10 &Day
& 11 10 &Rainfall (mm)
&END HEADER
#Date - 01011992
      1.05     1.300
      1.10     0.000
      1.15    10.500

If you wish, you can store ancillary data in both types of .climate files. For instance, in the example below, streamflow data has been stored in the far right column of a type 2 data file. This can be useful later when comparing observed and predicted hydrographs using Topog_chart. 

&HEADER
&  1 10 &Day
& 11 10 &Rainfall (mm)
& 21 10 &Streamflow (m3/day)
&END HEADER
#This is inserted comment number 1
#This is inserted comment number 2
#Date - 01011992
      1.05     1.300     123.67
      1.10     0.000	 210.00
      1.15    10.500     240.00

Similarly, any number of comment lines (beginning with a '#') may be inserted between the header and data, as shown in the example above.


5.5.2 Generating a type 1 .climate file with Topog_climate

The climate simulator module, Topog_climate, can be used to generate vpd and radiation data from daily maximum and minimum temperature data. Adapted from models described by Running, Nemani and Hungerford (1987) and Bristow and Campbell (1984), Topog_climate can also scale temperature, radiation and rainfall data from one station to another which may have a different elevation or annual rainfall. This climate simulator only works for a type 1 .climate file.

Topog_climate expects tabulated data to be supplied in a free format .ppt file. The .ppt file can contain header or comment lines connoted with a "#" or "&" character in the first column. The data must be ordered in the following way:

  • day number (indexed to 1/1/reference year)
  • daily maximum temperature (oC)
  • daily minimum temperature (oC)
  • total daily rainfall (mm/day)

For example, the first few lines of a typical .ppt look like this: 

# This file contains data from field station 2
& Period of record is 28/02/1992 - 05/09/1994
	59   12.00	6.60	27.3
	60   15.40	8.00	0.0
	61   17.80	6.00	0.0

Note that it is not necessary for the .ppt file to begin on day 1 of a year, but the day number must be indexed to day number 1 of the reference year.

To run Topog_climate, type: $ _climate

and supply the .ppt file basename.

Next, provide the date (ddmmyyyy) corresponding to the first data record.

The program will then prompt for the elevation and mean annual rainfall of the base station site (ie. where the .ppt file data is from) and the modelled site (ie. your catchment). Both of these inputs will be needed to scale the temperature and rainfall data, if required. Elevation data is also needed for atmospheric transmissivity calculations. If you do not want to scale the temperature and rainfall data, supply identical values for the base and modelled sites.

Next, you are asked to provide values of the b and c parameters; these are the empirical coefficients used in the Bristow and Campbell (1984) equation. By changing the default values supplied, you can raise or lower the radiation estimates the program makes.

Next, you are asked to supply transmissivity coefficients for summer, autumn, winter and spring; these can be adjusted to optimise the seasonal pattern of radiation that is estimated by the program.

Finally, you are asked to provide the threshold rainfall and minimum transmittance; here you can instruct the model to reduce transmittance to a minimum value on days exceeding the threshold rainfall value.


5.5.3 Generating a radiation coefficients file with Topog_rceoff

If you are using a type 1 .climate file, then you will also need to generate a radiation coefficients (.rcoeff) file. This file contains information of how to scale flat surface radiation (as found in the .climate file) to catchment elements with discrete slope and aspect values. This file is built using program Topog_rcoeff.

To run Topog_rcoeff, type: $ _rcoeff

and supply the site latitude in degrees, using a "-" sign for sites in the southern hemisphere, and a "+" sign for site in the northern hemisphere.

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last modified on 24 June 1997