The solar radiation reaching the earth's surface on a given day, , may be less than due to the presence of cloud cover. The daily solar radiation data required by SWAT+ may be read from an input file or generated by the model.
The variable SLRSIM in the master watershed (file.cio) file identifies the method used to obtain solar radiation data. To read in daily solar radiation data, the variable is set to 1 and the name of the solar radiation data file and the number of solar radiation records stored in the file are set. To generate daily solar radiation values, SLRSIM is set to 2. The equations used to generate solar radiation data in SWAT+ are reviewed in Chapter 1:3. SWAT+ input variables that pertain to solar radiation are summarized in Table 1:1-2.
Table 1:1-2: SWAT+ input variables used in solar radiation calculations.
| Variable Name | Definition | File Name |
|---|---|---|
see description of .slr file in the User’s Manual for input and format requirements if measured daily solar radiation data is being used
SUB_LAT
Latitude of the subbasin (degrees).
.sub
SLRSIM
Solar radiation input code: 1-measured, 2-generated
file.cio
NSTOT
Number of solar radiation records within the .slr file (required if SLRSIM = 1)
file.cio
SLRFILE
Name of measured solar radiation input file (.slr) (required if SLRSIM = 1)
file.cio
ISGAGE
Number of solar radiation record used within the subbasin (required if SLRSIM = 1)
.sub