I also don't think the consequences as easy to predict as you think. For example cross crops may transpire less because of their pores being closed more due to higher CO2 concentrations. That may be good, depending on the crop and location. There will be higher flow in most rivers, and by association most lakes (but offset by higher evaporation) which could be good both for humans and irrigation. I think the answer is complicated and difficult to predict.
Current unsustainable practices with respect to both soil and groundwater depletion will still be unsustainable.
Parts of California are not a great place to grow crops sustainably, at least not the kinds of water and soil intensive crops currently grown. That may increase or decrease on the whole over time due to climate change, it's tough to say with any certainty.
The solution to California's droughts isn't just dams. You can't build a dam large enough to hold enough water for going multiple years without rainfall and the aquifers, which bank water in the ground were deeply depleted in the last drought.
A better way:
The moisture is being sucked out of some places and falling to others. So one area is becoming barren, and another is being flooded. This means a few things:
- It is harder to farm. Can't farm when it is flooded, can't farm when it is barren
- It is harder to keep fixed cities because the climate changes. Imagine having to move NYC every 10 years. It is far worse when people don't have good infrastructure.
- The displacement of people will make the syrian refugee crisis look pale in comparison to what is coming.
- Entire ecologies being destroyed is gonna be an economic hit we can barely comprehend.
- Extreme weather is another effect. Example being freezing temperatures mid-bloom. Or a hot week mid winter. Crops grow and freeze causing entire crop failures.
And fires are only gonna get worse. The fact that right now this tree survived is great. But will it in 10 years?