Not to get too much into politics here, but California has lots of people and lots of demand for water, yet very little water storage capability has been added over the last few decades. Every time a new reservoir is proposed groups of people oppose and it gets shut down. We know we have droughts and we know that every single year, even in the good years, there is a six month period where we get almost no rain. If during those good year winters we had the ability to store more water, then in these bad drought years we wouldn't have the problems we do.
And just for info, this won't be just a California problem. California's agriculture industry is a multi-billion dollar industry and supplies food all over the Country and the world. Agriculture also uses 80% of the water. If that water isn't there then all us are going to be paying some high prices at the grocery store in the coming months.