"If you go back thousands of years, you see that droughts can go on for years if not decades, and there were some dry periods that lasted over a century, like during the Medieval period and the middle Holocene [the current geological epoch, which began about 11,000 years ago]. The 20th century was unusually mild here, in the sense that the droughts weren’t as severe as in the past. It was a wetter century, and a lot of our development has been based on that.
If you look at the archaeological record, you see that the Native American population in the West expanded in the wet years that preceded those long droughts in the Medieval period. Then during the droughts, they were pretty much wiped out. There was the so-called Anasazi collapse in the Southwest about 800 years ago. In some ways, I see that as an analogy to us today."
Anyone who wasn't expecting a multi year drought in California obviously didn't study history.