1:1.2.3 Daily Solar Radiation

The solar radiation reaching the earth's surface on a given day, $H_{day}$, may be less than $H_{mx}$ 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 slr in the master weather station (weather-sta.cli) file identifies the method used to obtain solar radiation data. To read in daily solar radiation data, the slr variable is set to 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, set the name of the solar radiation input file (slr) to sim. 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.

Definition	Source Name	Input Name	Input File
Latitude of the solar radition station (degrees).	lat	lat	slr.cli
Number of solar radiation records within the .slr file	slrfiles		file.cio
Name of measured solar radiation input file (.slr) to simulate set to "sim"	sgage	slr	weather-sta.cli
Number of solar radiation record used within the subbasin (required if SLRSIM = 1)	ISGAGE		.sub

See the description for the .slr files on the slr.cli page for input and format requirements if measured daily solar radiation data is being used.