There are easier ways to deal with the drought than abandoning Los Angeles. For instance California could cut back its almond production:

http://www.slate.com/articles/technology/future_tense/2014/0...

From the article:

"California almonds use a stunning 1.1 trillion gallons of water each year, or enough for you to take a 10-minute shower each day for 86 million years (using a low-flow showerhead, of course)."

I think the answer is for California to embrace the fact that it's a post-agricultural society and refocus resources on its human capital rather than it's increasingly unproductive farmland.