You don't need to be a climatologist to figure this one out, just being a resident there you figure out very soon how flash flood areas are possible (specifically in SoCal) since every square inch is paved the rain water, when it actually falls, is destined to cause damage and/or make it's way to the gutter system: often overwhelming the drains depending on the area. It doesn't seep into the Earth to replenish the aquifers because everything is paved relative to just undeveloped land.
This is an entirely absurd missed opportunity to build the infrastructure for water reclamation, and while we're at it the Australian model to extract the waste water and reclaim it and create fertilizer for plants from human waste should be explored as well. The money is there, and a need for jobs is, too.
Even if CA were only to spend 50% of the ~$90 Billion it would still be able to do a great deal to ensure it's longterm future by investing in this critical infrastructure.
* There used to be a running bet of what celebrities mansion in Malibu would end up sinking into the Pacific when i was a kid in the 90s as it was so common back then. It was a Schadenfreude based bet with more amusement than just playing the lotto apparently. Incidentally enough, those homes were soon replaced with another the following year(s) anyway more often anyway.
