Huh? We've got the best farmland in the US, possibly the world. It'd be a terrible shame not to take advantage of it.
All of which is irrelevant to the wine conversation, because the relatively dry climate is exactly what makes the Napa and Livermore valleys some of the best in the world to grow grapes. You've got good soil, dry summers allowing for control over how much water the grapes get that make them grow more flavorful, and very few frosts. The fact that the region gets almost all of their rainfall during the winter also helps avoid the grapes going to mold.
They have to pump water OUT of their fields and pay for the privilege of doing so as opposed to pumping it in from an irrigation canal.
Nothern California has no shortage of water whatsoever, and indeed it’s a regular news item whether or not to divert a few million extra gallows into the ocean to sustain some variety of fish that likes to swim around in the delta.
Even if there was an extreme drought, putting water in people's bodies via drinking should never be curtailed.
(though maybe stop watering crops with brawndo)
It gets hot here, but Temecula gets a breeze from the ocean that makes it somewhat tolerable for growing grapes. The wines were tend to be the high-alcohol variety (think cabs and zins) because those are what grow better in the heat.
Most of the wines here aren't that good, but the wineries are more the attraction because they're beautiful and a short drive from LA, SD, or Palm Springs. Popular for weddings and bachelorette parties.
(There are some wineries here doing interesting things but if I'm buying wine to consume at home I'm usually looking for other regions than my backyard).