Running Lisem

All input and output maps in openLISEM are in the PCRaster format. PCRaster is a GIS and modelling language produced by PCRaster environmental software. openLISEM needs a long list of maps to run. There is a minimum number of maps when you run it only as a runoff model. If you include erosion, special soil surfaces, flooding or other processes, more maps are needed. The easiest way to create the maps database is by using the PCRaster script. This uses a few base maps and a few tables with soil and vegetation properties to create the full database.

The philosophy of openLISEM is keep the input database as flexible as possible, and to use te input maps directly in the equations in the model. For instance: the DEM is not used directly in the model but only the derivative maps “slope gradient” and “flow network”. This allows the user to put his/her own slope map directly in the model, such as when you want to simulate teracces with a much lower slope angle than is calculated form the DEM. Also the maps of soil, soil surface and vegetation properties can be derived from classified maps, or from a continuous spatial interpolation, or a mix of the two. Thus here are as many input maps as there are variables in the equations. This has often been critisized, but we prefer this above all kinds of obscure and empirical derivatives that are hardcoded in the model.

IMPORTANT: it is the responsibility of the user to create a logical database. For instance the user can combine a dense veegation cover map with a very low flow resistance map (Manning’s n), the model will not warn that such a combination cannot exist in reality. This might even exist: a dense grass can be traversed by wheel tracks that allow the runoff to pass quickly! We want the user to have maximum freedom and assume the user knows what he/she is doing.

Installation and creation of the database

The easiest way to explain how to make a database is by using the PCRaster script and cerating a database.

  • Download and install PCRaster first: here.
  • PCRaster is in principle a command line driven system without an interface. However for Windows a shell has been developed called NutShell: download here and install.
  • The script is a simple text file that is interpreted by the PCRaster program pcrcalc.exe. Download the lisem database script here. Make a directory where your database is going to be created (e.g. “\data\maps”) and copy the cript in there
  • Download the zip file with basic maps and tables that you need to run this script here, and unzip them to the same directory (“\data\maps”).

After installation, open nutshell (nutshell) and make sure that the pcraster installation is found (file->options). Go in NutShell to the directory where you have downloaded the script and load it in the editor.The example used here is from a runoff and flooding project in Kampala, Uganda.

Importing form other GIS systems

If you have data from other GIS systems you can convert this to PCRaster. There are 3 steps involved:

  1. In PCRaster you have to make to make a “clone” map that has the correct rows, columns and coordinates;
    In NutShell click on the mapnew icon and fill in the correct data in the popup window, choose increasing or decreasing y-coordinates depending on your database. NOTE: if you have a PCRaster database already you can use any map as a clone, you don’t have to make it, e.g. the DEM will do.
  2. In your GIS, you export your maps to ascii maps, most GIS systems can do that. An ARCGRID export map looks like this:
    ncols 788
    nrows 726
    xllcorner 449198.1803
    yllcorner 35531.6741
    cellsize 10
    NODATA_value -9999
    -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 etc.
    -9999 3 3 5 5 5 5 5 6 etc.
  3. You import the map into PCRaster using the asc2map command and the clone map. The command is (-a is used for arcgrid maps):
    asc2map -a –clone mymap.txt

See here for further information on improting mapsinto PCRaster.