Where California Grows Its Food

By Geoff McGhee

Throughout the West, agricultural management and water management are closely intertwined, perhaps nowhere more so than in California. During much of its growing season, the weather turns bone-dry. The state has nearly 40 million residents, yet the Department of Water Resources’ biggest client is agriculture – irrigation claims as much as 80 percent of all water used for businesses and homes. It is DWR that holds the taps of dams and aqueducts delivering that water.

Stockton, We have a Problem: Groundwater Overuse

But during the historic drought of 2011-15, water deliveries turned to a trickle, and in some years stopped entirely. To keep their crops growing and livestock watered, farmers and ranchers pumped record quantities of groundwater instead.

In 2014, as aquifers dropped precipitously, legislators enacted the state’s first-ever groundwater regulation. While DWR has always considered groundwater use, the Sustainable Groundwater Management Act (SGMA) would require a much closer eye on groundwater pumping. One of the best ways to know how much water farmers need? Know what they grow.

An Extremely Detailed Map of California Crops

The water resources department had done regional crop surveys in the past, and the federal Department of Agriculture publishes some general land use data, but these had limited utility in figuring demand for water. “We had our ongoing land use program and our efforts for the water plan,” said Curtis Anderson, a regional head for DWR, “but it was really the drought and SGMA coming together that pushed it over the edge and we said, ‘ok, let’s do this.’”

By “this,” Anderson means the most detailed survey ever done of crops and land use in California. It covers nine million acres of land devoted to grapes, alfalfa, cotton, plums, you name it – food for people and animals all over the world.

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How Did They Do It?

It takes a lot of technology to survey millions of acres spread over thousands of square miles. To assemble this portrait of California’s agricultural patchwork, DWR and their consultants, LandIQ, made extensive use of satellite and aerial imagery, aka “remote sensing.” “It’s the first time that remote sensing was used to this extent in one of our base maps,” said Muffet Wilkerson, who works in DWR’s integrated water management unit.

Wilkerson said surveyors began by traveling around the state collecting “ground truth” samples, which they fed into a software system – “there’s a big broad-brush that classifies [crops] in a sort of automated way.” Part of the ground truth data served to “train” the classification system, and another part was used to validate the results.

The map is “pretty darn good,” said Wilkerson, “but it is only a model of reality. And it is also based on people having visited these spots, and sometimes on maps that are already available,” she added.

A Moving Target – Year to Year, and Month to Month

This map is based on a single snapshot of California’s agriculture, in June and July of 2014. So the Imperial Valley’s winter lettuce has already given way to other cash crops, and strawberry fields around Salinas and Watsonville may already have been be winding down. Also, land marked here as “idle,” said Wilkerson, “doesn’t mean that it was completely taken out of production. It could have been just temporarily fallowed between two crop rotations.”

Which brings us to a central limitation of the data: it can’t tell you what crops are on the rise (like almonds and other tree nuts), or on the wane (such as crops on land where saltwater has seeped into the groundwater). But after starting out as a one-off in 2014, the crop survey was given dedicated funding by the passage of the 2018 state water bond, Proposition 68. Currently, DWR is working on a map of 2016 data, which they say should be ready by mid-2019. And, said Wilkerson, “the ground-truthing portion of the 2018 survey is happening now.” She added, “2018 will be the first one that includes a multi-season picture of the year.”