I know a Walnut grower and an Almond grower, this whole concept is a load of shite!
You can't just whimsically decide not to grow Walnuts or Almonds because water has been tight for 4 years, these orchards take 20+ years to become fully mature.
The idea that Almond or Walnut growers are choosing those nuts like you choose a different colored filament for a 3D printer is ludicrous.
The other problem with this notion is that they want to yet again increase the price of water, what California needs to do is stop giving all their damn water to the cities and return it to the farmers. California had plenty of water before the cities got overgrown and portly.
Stop making a bunch of useless new legislation, stop growth in big cities, encourage farming, and stop stepping on individual rights!
(A former Californian who can't stand how the state has become)