I hope I get your question clearly. From what I read the data your are talking of are all meteorological/climate data. SWAT does not allow the input of gridded meteorological/climate data but you can create what is called virtual stations using the mid point of the grid and then generate the time series for each location like you would do for any climate station by extracting the data from the daily or monthly grids with the values into tables and load them into SWAT as stations and then model with them. I hope you get me?

SWAT allows to input point meteorological stations in order to generate discharge forecasts. Thus, it is difficult to use the method that Mr. Adjei is proposing (too many stations if the grid cell size is too small).