Comment by saltcured

Not necessarily... it isn't as straightforward as "stronger El Niño means more rain".

The steering of the jet stream seems to have some qualitative changes in these conditions but also more chaos. It could steer storms anywhere along the coast, so different parts of CA, OR, and WA get different impact. Just in my lifetime in CA, I've witnessed some very wet El Niño winters but also some drier than average.

The biggest precipitation threat on the west coast seems to be a repeat of some of the biggest flooding events known historically or geologically. But, these are relatively infrequent and most of the record predates any understanding or tracking of the El Niño oscillation. So the correlation cannot be stated so clearly. These are atmospheric river events which seem to stall, producing heavy rains over the same area for a much longer period.

Just in the recent centuries of CA history, there have been massive floods in northern and southern regions in different month-long rain events. There have been improvements to flood control infrastructure since then. But, the only reason those events aren't known as the most costly is because there wasn't as much economic development here back when the floods happened.

Our usual storms sweep through an area the heaviest rains over just part of a day. Our varied terrain means that each individual storm also has very uneven rainfall amounts due to orographic intensification. Prominences with the right aspect towards the wind will get far more accumulation. Our watersheds can absorb quite a bit of this, but even those brief rains can cause localized flooding.

If the rain continues for many days in a row, we will see widespread mudslides and flooding of larger rivers, basins, etc. Some of the historically extreme events had rain persisting for over a month!

Edit: along with these "mega storm" scenarios, we also have evidence of "mega droughts". It's worrisome to imagine what challenges may come from a more energetic and chaotic climate.