Please i need assistance on how to link the two models, because i am planning to couple them and assess water availability in a basin with scarce data

Hey,

If you know some programming, I think that the easiest way is that you writing platform in VBA, and then link software to each other, for instant Excel.
you can run SWAT and then send its output to some specific cells in Excel and then run WEAP by getting this cells as inputs.

Just remember that WEAP can not run for the next time step. Everything that you can do is on current time step.

If you have enough time and have good knowledge of programming, I think that it is not bad to take a look to this stuff, too:

http://www.openmi.org/

Cheers,
Mehdi