Re: How do I stop the rain from coming down to my patio from my deck above?
You can use temporary outdoor carpet [not recommend] or install awing / roof .
I would not close the gap between the wood plank. The gap is there for wood expansions during weather change.
Even if you reduce the gap, the rainwater will go through anyway.
"Life does not go by the book, we learn as we go along".
You only need two tools in life - WD-40 and Duct Tape.
If it doesn't move and should, use WD-40.
If it shouldn't move and does, use the Duct Tape.