DB2GRD

Purpose:

The module DB2GRD is used to generate the nation-wide SURFER grid files with model results directly from the daily rainfall and monthly evaporation records previously prepared under rainfall pre-processing respectively evaporation pre-processing modules.





Note: The following description refers only to the operation of the module by the user. The internal calculation steps are visualised by a flowchart.

Data requirements:

Rainfall database: Tables jRain and rainstat of an Access database (typically with name rainfall-offline.mdb).

Evaporation database: Tables mETP and climstat of an Access database (typically with name evap-offline.mdb).




System data: A directory containing the basic map grids hssoil.grd (surface CN-values) and hgsoil.grd (percolation CN-values) as previously calculated with the model builder module. Also the grid file flatland.grd and the blanking file nation.bln must be in that directory. As a standard, these grids should be in JTM and have a resolution of 2000 m.

The location of these files can be freely selected, but they should be on the same computer and not on a network drive.

Required user inputs:

Calculation period. The dates from and to have to be set manually. Generally it is recommended, to start at the beginning of a water year (i.e. 01 October) and to end at the end of the rainy season (i.e. 31 May). For the period 01 June to 30 September no calculations will be performed performed.

Interpolation grid size. In order to speed up the spatial interpolation, an option is set to use a more coarse grid. Different grid sizes can be set through a pull-down menu. A proposed value is 4000 map units (= Metres). Afterwards, the resolution is very efficiently improved by the program through the spline smooth function.

Modelling grid size. For modelling, the resolution must be equal to the resolution of the grid files generated from maps (HSsoil.grd and HGsoil.grd). Presently, the number of 2000 m is used and it is not recommended to change this. Note: If, for calibration purposes, a lower resolution (= larger grid size) is required, the files (HSsoil.grd and HGsoil.grd) need to be recalculated accordingly! This procedure of data pre-processing can be done with the model builder, but presently it is "hard-coded" and not an option to be changed by the user.

"Delete daily grid files" - yes or no. In order to save disk space, daily grid files should be deleted automatically when not needed further. However, the check-box option permits to keep daily results for instance for flood periods of particular interest.

The option monthly / daily evaporation data is currently disabled, only monthly evaporation data have been calculated in the database.

Rainfall database. Indicate the path containing the rainfall data base. Usually the path shown does not need to be changed.


Evaporation database. Indicate the path containing the evaporation database. Usually the path shown does not need to be changed.

Result path. The name of the result path should be in accordance to the system data path. A directory name Runoff20k12  indicates the use of map system data Map20k12.

System data. The name of the system path should be mnemonic. A directory name Map20k12 will indicate a grid size of 2000 m, Curve number version #12.
If you enter a path name without the required data, the program will give a warning.





After all inputs have been set, execution can be started pressing the key "Start Modelling".


The processing consists of 3 different steps:

1. Generation of temporary ASCII text files for spatial interpolation of rainfall and evaporation under Surfer. This process cannot be interrupted. The progress is indicated at the lower left corner of the form:
   
   
   


2. The actual modelling of daily rainfall, runoff and percolation and accumulation to monthly and annual totals.

   The theoretical background and sequence of calculations are explained separately.

   The form is periodically refreshed, and indicates the calculation process by a message in the lower left corner of the form: modelling: dd/mm/yyyy.
   
   
   Once started, the process can be interrupted by pressing the key "Pause".
   
   On pressing this key, first the calculation of the day currently processed will be completed. Afterwards, a message pops up at the lower left corner of the form indicating "Interrupted after processing: dd/mm/yyyy"
   
   The former Pause-button now reads "Resume at dd/mm/yyyy"
   
   and can be used to continue the calculation process.
   
3. At the end of the calculation, an automatic cleanup takes place, i.e. the removal of ASCII files and temporary grid files.
   Once the process is completed, the message "done" is shown at the lower left corner of the form.

Module output:

SURFER grid files (in binary Surfer 7 format) for rainfall (r*.grd) , direct runoff (q*.grd), deep infiltration (i*.grd) and actual evaporation (e*.grd). The units of the grid values are Millimeters. The grids cover the entire country; for division into basins or catchments as well as calculation of volumes the post-processing module is required.

Usually monthly and annual data are produced, on demand also daily grids are maintained. The annual data are for hydrological years. For Jordan, this is the period from October to May.