There are a lot of hand-waving, speculative answers in the responses to this question, but the reality of the answer is that it actually goes far beyond what is happening in just California.

Firstly, I think its important to note that everything you cite as an issue in California is happening writ large across the United States. Every issue you cite is repeated again and again in every productive economic center across the United States. Absurd rents/ housing prices/ CoL, devastating issues with homelessness and drug abuse, increasing devastation from climate related weather issues. California stands out as particularly addressable because for better or worse (or due to the sierras and the southern desert), California is a bit of an island unto its self.

I grew up in southern California and watched the impacts of the 2007-2009 economic collapse in real time. I was extensively involved in activism related to homelessness at the time. I watched families and communities become absolutely devastated by the economic (and resulting homelessness and drug abuse that inevitably follow) fallout from those events. To summarize, California (and the US through analogy), never actually recovered from the 2008 crisis. The families that fell during that time never really got up again. Working class (labor) families went from thinking they could support their first and second children through community college and eventually four year university, to barely scraping by or living in slow decline. The vast majority of families impacted by the 2007-9 economic collapse never actually recovered, and have basically limped along or tread water since then.

The result has been an ever increasing disparity between the rich and the poor in California. In few places is this as well displayed as in the Bay area. The amount of wealth that has accumulated there is almost preposterous; and yet, it fails to hide an utter epidemic of homelessness and the problems that accumulate in its presence.

Several in this thread cite governance issues in the state of California. I call bullshit on this. The reality is that California is a huge and complex state with more economic activity than most countries. It shouldn't surprise you that it requires a complex bureaucracy to respond to that.

Very simply, the US stopped taxing or regulating wealth in the mid-late 2000's, and in the post 2008 era made it clear it had no intention of holding any one accountable for their actions in financial markets. Almost everything you see politically, socially, and economically in the United States is a direct consequence of that era.

Its my opinion is that the US is in serious decline and on a random walk towards a failed state (if it isn't there already? how do you define a failure mode for a country?). The US is unable or uninterested in taxing wealth or its highest income earners, and as a consequence, the wealth curve has gone asymptotic. The distribution of wealth in a society is key to its stability, and as the kurtosis becomes more and more positive, people begin to lose any incentive to participate.

The solutions to these problems are quite simple and no new technology is required to implement them. Return to a 90% tax burden on highest income earners and tax wealth directly. Force billionaires to spend their money or lose it. IF they want to take their ball and go home, then they lose their seat at the playground. The US has had policies like this in the past and they've shown their effectiveness.

In regards to the specific drought issue, the state was effectively plumbed during an abnormally wet era. What you are seeing here described as 'drought' is not too far off from the historic norms. Coupled with drought, California is also seeing its wettest years on record (2017/18), but due to climate forcings, its all rain and no snow.

I think the final emphasis that I would like to place is that what is happening in California is repeated all across the United States. Climate issues, housing prices detached from reality, homelessness and drug addiction running rampant, and no ability or will from the political apparatus to respond to these issues.