In 2013, California state GDP amounted to $2,220 billion, of which $46.4 billion (2.1%) was contributed by agricultural commodities. All other output amounted to $2,173.6 billion (97.9%).
In 2013, urban use of water amounted to 8 million acre-feet (AF), about 10% of state water resources. Irrigated agriculture consumed 23.9 million AF (41% of total), while environmental usage took 29.2 million AF (49% of total).
California agricultural statistics can be found here. In 2013, the top 20 commodities ranged from a high of $7,618 billion for milk and cream to a low of eggs and chicken of $380 million. But water usage does not correlate with the dollar value of output of each of these commodities.
Blaine Hanson in the Department of Land, Air and Water Resources at the University of California, Davis charts water use of California crops on page 4 of his report.
Here are a few shocking calculations.
Alfalfa amounts to $1.57 billion of output using 5.3 million AF of water. Divide the value of output by the amount of water used yields $296 per AF.
Rice output is valued at $790 million, using 2.7 million AF of water. This amounts to $293 per AF.
Cotton output is valued at $623 million, using 2.3 million AF of water ($271 per AF).
All other non-agricultural state output amounts to $2,175 billion. Using only 8 million AF yields output valued at $271,875 per AF. Urban use produces 925 times as much output value as each of three of agriculture's most thirsty crops. (Except for pasture, all other cash crops produce higher valued output per AF of water than alfalfa, rice, and cotton.)
Alfalfa and rice use as many AF of water as all urban usage. It is true that urban water usage can be made more efficient, enough to meet Governor Brown's statewide mandatory reduction of 25%.
But what if the drought continues for 1, 2 or more years? Should California continue to allocate 8 million AF of water to growers of hay and rice? This makes no sense, never mind historical rights. It's vital that the state legislature get cracking with a comprehensive overhaul of water usage (the Australian solution would be a good place to start) so that it can enact legislation if the drought continues through the 2015-2016 rainy season and beyond.