2  Input files

The input data of SWAP are divided over 4 different file types:

• Main input file (*.swp)
• Meteorological file (*.met, *.rain or *.yyy)
• Crop growth file (*.crp)
• Drainage file (*.dra)

Appendix A provides an overview of the information in these input files. The main input file and the meteorological data file are always required. Input files of crop growth and drainage are optional. The extensions of the files are fixed. The names of the input files are free to choose and are specified in the main input file. As listed in Appendix A, the main input file contains general information with regard to the simulation, meteorology, crop rotation scheme, irrigation, soil water flow, heat flow and solute transport. For meteorological data, commonly a file with daily data is used, but also more detailed input of evapotranspiration and rainfall fluxes is possible. The detailed crop growth input file is required to simulate crop development and biomass assimilation. As an alternative, the development of crop parameters such as leaf area index or rooting depth can be prescribed in the simple crop growth input file. The drainage input file contains two sections. The basic drainage section provides input for drainage towards ditches and/or drains. The extended drainage section provides input for drainage including simulation of surface water levels.

Tip 2.1: Formt example of SWAP input files.

**********************************************************************************
* File name
  METFIL = 'hupsel.met'      ! File name of meteorological data, in case of yearly files without extension .YYY, [A200]
                             ! Extension is equal to last 3 digits of year, e.g. 022 denotes year 2022
                             ! In case of meteorological in one file use extension .met

* Details of meteo station:
  LAT = 52.0                 ! Latitude of measurement site [-90..90 degrees, R, North = +]

* Type of weather data for potential evapotranspiration
  SWETR = 0                  ! 0 = Use basic weather data and apply Penman-Monteith equation
                             ! 1 = Use reference evapotranspiration data in combination with crop factors

* In case of Penman-Monteith (SWETR=0), specify:
  ALT = 10.0                 ! Altitude of measurement site [-400..3000 m, R]
  ALTW = 10.0                ! Height of wind speed measurement above soil surface (10 m is default) [0.1..99 m, R]
  ALTH = 2.0                 ! Height of humidity and temperature measurement (1.5 m is default) [0.1..99 m, R]
  
  ANGSTROMA = 0.25           ! Fraction of extraterrestrial radiation reaching the earth on overcast days (0.25 is default) [0..1 -, R]
  ANGSTROMB = 0.50           ! Additional fraction of extraterrestrial radiation reaching the earth on clear days (0.50 is default) [0..1 -, R]

* Switch for distribution of E and T:
  SWDIVIDE = 1               ! 0 = Based on crop and soil factors
                             ! 1 = Based on direct application of Penman-Monteith

* In case of SWETR=0, specify time interval of evapotranspiration and rainfall weather data
  SWMETDETAIL = 0            ! 0 = Time interval is equal to one day
                             ! 1 = Time interval is less than one day

* In case of daily meteorological weather records (SWMETDETAIL=0):
  FWIND = 1.0                ! Factor for converting 24h averaged windspeed to daytime average windspeed (7-19h; default 1.0) [0.5..5 -, R]

* Switch for use of actual rainfall intensity (only if SWMETDETAIL=0):
  SWRAIN = 1                 ! 0 = Use daily rainfall amounts
                             ! 1 = Use daily rainfall amounts + mean intensity
                             ! 2 = Use daily rainfall amounts + duration
                             ! 3 = Use detailed rainfall records (dt < 1 day), as supplied in separate file

* If SWRAIN=1, then specify mean rainfall intensity [0.d0..1000.d0 mm/d, R] as function of time [0..366 d, R]
  RAINTB =
    1.0  20.0
  360.0  40.0
* End of table

* If SWRAIN=3, then specify file name of file with detailed rainfall data
  RAINFIL = 'hupsel.rain'    ! File name of detailed rainfall data without extension .YYY, [A200]
                             ! Extension is equal to last 3 digits of year, e.g. 003 denotes year 2003
                             ! In case of rainfall in one file use extension .rain

**********************************************************************************

Tip 2.1 gives an example of a part of the *.swp input file. General rules for the format of input files are:

• free format with the structure ‘variablename’ = ‘value’ or in a table with variable names in the first line;
• order of variables is free;
• comment in lines is allowed starting with ‘*’ or ‘!’;
• blank lines are allowed;
• tabs are not allowed.

In the input files, of each parameter the symbolic name, a description and numerical information is given. The numerical information between square brackets consists of:

• range
• unit
• data type

For example: [-5000 .. 100 cm, R] means: value between -5000 and +100 with a unit in cm, given as a Real data type. In general SWAP uses for time the unit DAY and for length the unit CENTIMETER. These are practical units for soil physical quantities and fluxes. Exceptions are meteorological data such as rainfall, irrigation and evapotranspiration, which are specified in MILLIMETER. In case of real data, the number should at least include a dot. Other data types are integer and character.

In case of data series as function of time or depth such as groundwater levels or initial pressure heads, SWAP will apply linear interpolation. Outside a specified range, the closest value will be adopted. For instance in Tip 2.1, the rainfall intensity (rainflux) will gradually increase from 2 to 4 cm d^-1 between t = 1.0 and t = 360.0. At t > 360.0, the rainfall intensity will be 4 cm d^-1.