Under the heading of Things You May Not Realize'. I noticed that I was having a buildup of water on my patio from recent rains. I knew that with El Nino stirring things up and predictions of more rain that wasn't a good thing.
So, I called in my plumber who came to the conclusion that a tree root must have plugged up the pipe underground and that was keeping water from spilling out onto the street. I called the gardener who plans to come out and dig up the area around the tree and fix the problem.
I mention this because roots and things underground that we can't see can create some serious patio flooding as heavy rains fall. So, for your El Niño checklist, you might consider checking your patio and other area drains. Glad I did.