California farmers make a lot of hay. Until 2013, they used more land to grow alfalfa for hay than any other crop. Now, alfalfa uses the second-most acres behind almonds. Most CA alfalfa hay is used to feed cattle, although up to a third of it is exported to Asia.
Although it remains the second-most grown crop in the state, alfalfa acreage has declined by almost 50% since its peak in 2000. Comparing satellite data from 2010 to 2020, we see substantial declines in alfalfa acreage in the southern Central Valley, where it has been replaced in large part by grapes, almonds and pistachios. (The images below are static. Go to our Cropland Data Layer app to play with the settings.)
Alfalfa, or lucerne as I knew it growing up, is a perennial crop that farmers usually grow for 3-5 years at a time. As a legume, it is highly nutritious and has deep roots that make it resilient in dry climates. CA farmers cut it for hay 6-8 times per year.
Alfalfa uses a substantial amount of irrigation water, though not substantially more than other perennial crops such as almonds, citrus, and pasture. Perennial crops use more water than annual crops because they grow year round, rather than only in the summer.
The plot below shows two sources of data on irrigation water applied per acre. The DWR data come from the CA Department of Water Resources, which models water use based on data including evapotranspiration, soil characteristics, precipitation. and irrigation efficiency. They show more water applied in the drought years of 2013-14 for most crops. The Census data come from 2013 and 2018 Censuses of Irrigation. DWR shows somewhat higher water use for alfalfa and lower water use for rice.
Between 30 and 60% of California water goes to agriculture, depending on rainfall. Only about 10% goes to urban users, who typically are willing to pay much more for water than are farmers.
Alfalfa acres are declining in California because other crops, especially tree crops and grapes are more profitable. However, if those acres are replaced by almonds, this is unlikely to free up much water for urban users. Nonetheless, there is a lot of promise for AI technology to improve water use efficiency.
I made the bar chart using this R code.