your porches are not on any "fall". There needs to be a down hill slant or fall away from the house so the water will run off the porch away from the house.
Then, there should have been, some four inch angle flashings built in at the intersection of the porch floor and the exterior home walls.
To create a fall would be quite disasterous to your home and the home. Meaning, the doors would be off, the structure would have to be re vamped.
Is there a way to pry up the decking boards by the walls and slide some shims or furring strips between the decking and the joists to creat a fall? You might have to adjust your thresholds for the doors since the rise would make the doors not open.