there is no proof whatsoever yet he proclaims it with great confidence much like other liberals say "hands up don't shoot" and "Romney paid no taxes" with great confidence. The water shortage comes from a 60% increase in population in the last 30 years, no new reservoirs , and
letting 70% of rain water run off into the ocean.
Jerry Brown's lie seems especially egregious since, 1) it is a lie to absolve himself and liberals for responsibility for the shortage, and 2) it is a very dishonest way to promote global warming.
Here maybe all these articles on climate change and drought will help you not sound so stupid.
climate change drought - Google Scholar