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Simulation Settings

There are three files that control the settings for a simulation run:

object.cnt specifies the land area and the total area (including ponds and reservoirs) of the watershed and the counts of all spatial objects in a simulation,
time.sim controls the simulation time period and time step, and
print.prt controls which output files will be printed for a simulation.

An additional, optional file, object.prt, allows the user to print selected output for individual spatial objects.

object.cnt

This file specifies the land area and the total area (including ponds and reservoirs) of the watershed and the counts of all spatial objects in a simulation.

Field

Description

Type

time.sim

This file controls the simulation time period and time step.

Field

Description

Type

day_start

Beginning day of the simulation

SWAT+ is able to begin a simulation at any day of the year. This option can for example be useful, if the user wishes to simulate hydrological years instead of calendar years.

If day_start = 0, the model will start the simulation on January 1st.

If the simulation begins before the first day of the observed climate data, SWAT+ will use simulated climate data for the time period before the start of the observed climate data.

yrc_start

Beginning year of the simulation

If the simulation begins before the first day of the observed climate data, SWAT+ will use simulated climate data for the time period before the start of the observed climate data.

day_end

Ending day of the simulation

SWAT+ is able to end a simulation at any day of the year. This option can for example be useful, if the user wishes to simulate hydrological years instead of calendar years.

If day_end = 0, the model will end the simulation on December 31st.

If the simulation begins before the first day of the observed climate data, SWAT+ will use simulated climate data for the time period before the start of the observed climate data.

yrc_end

Ending year of the simulation

If the simulation ends after the last day of the observed climate data, SWAT+ will use simulated climate data for the time period after the end of the observed climate data.

step

Time step of the simulation

SWAT+ is able to run at the following time steps:

Code

Time Step

When using the Green & Ampt method (gampt in codes.bsn) for calculating surface runoff, the time step of the precipitation data must match the simulation time step.

print.prt

This file controls which output files will be printed during the simulation.

The print.prt file is formatted differently than most other SWAT+ input files (see figure below). In line three, there are several variables for controlling the time period to be printed. In line five, the user can specify the number of print intervals for average annual output. In line seven, the user can select to have output files printed in a specific file format (in addition to the default *.txt output files). In line 9, the user can control the printing of outputs for soils and management as well as flow duration curves. In lines 11 to 90, there is a list of outputs for different spatial levels and objects that can be printed at daily, monthly, yearly, and average annual time steps. A description of the output files is provided in the SWAT+ Output Files section.

Field

Description

Type

nyskip

Number of years at the beginning of the simulation to not print output

Some simulations will need a warm-up or equilibration period. The use of a warm-up period becomes more important as the simulation period of interest shortens. For 30-year simulations, a warm-up period is optional. For a simulation covering 5 years or less, a warm-up period is recommended.

Examples: If nyskip = 2, the model will skip printing the first two years regardless of the starting year. If nyskip = 0, output for all years of the simulation will be printed. If nyskip equals the number of years in the simulation, no output will be printed.

interval

Print interval within the period

This parameter specifies the interval within the specified printing period.

Example: If interval = 2, output will be printed for every other day.

aa_int_cnt

Number of print intervals for average annual output

If aa_int_cnt = 0, the model will print average annual output for the entire period. If aa_int_cnt > 0, the end years of the print intervals have to be specified by the user by listing them in chronological order in the same line as aa_int_cnt.

Example: If aa_int_cnt = 3 1955 1965 1975, average annual results will be printed for the time periods ending in 1955, 1965, and 1975.

object

Objects that output can be printed for at different time steps

The table below lists the objects that are listed in the first column of this section of the print.prt file. For each of these objects, output can be printed at daily, monthly, yearly, and average annual time steps by entering y (=yes) or n (=no) in the following four columns.

The user is advised to print only those outputs that are needed for model evaluation or further analysis. Especially daily printing can result in very large output files that may exceed hard drive storage.

Object

Definition

object.prt

This file allows the user to print selected output for individual spatial objects.

The object.prt file is commonly used to:

Print daily channel outflow to compare to observed streamflow a stream gage
Print daily flow to a file that can be read in as a point source from another SWAT+ simulation

The only timestep output can be printed at using this file is daily. A description of the output files is provided in the SWAT+ Output Files section.

Field

Description

Type

obj_typ

Type of object to print output for

Output can be printed for the following types of objects:

Object Code

Description

obj_typ_no

Number of the object to print output for

Soil water contents of the soil layers can be printed for all HRUs in the same file by setting obj_typ_no = 0. For all other outputs, a separate object print record with a unique name has to be defined for each object.

hyd_typ

Type of hydrograph to print

The following hydrographs can be printed:

Hydrograph Code

Description

Object type

Simulation Settings

object.cnt

time.sim

day_start

yrc_start

day_end

yrc_end

step

print.prt

nyskip

interval

aa_int_cnt

object

object.prt

obj_typ

obj_typ_no

hyd_typ

day_end

yrc_start

interval

nyskip

day_start

aa_int_cnt

Simulation Settings

yrc_end

obj_typ_no

step

print.prt

object.cnt

time.sim

object.prt

object

obj_typ

hyd_typ

hydcon