UC Berkeley study shows limited risk from permitted cannabis farms, questions illegal growths
Legal cannabis grow farms represent just about 20 to 25 percent of total weed farms in California, according to Ted Grantham, assistant professor at University of California Berkeley and co-director of the school’s cannabis research program. This means a significant amount of plantings are unregulated—the black market continues to thrive four years into the legal cannabis system.
Using aerial photography, Grantham and his fellow Berkeley researchers were able to quantify the extent of that black market. While California only has 8,000 permitted cannabis farms, scientists mapped 15,000 in Humboldt County alone.
However, according to the California Department of Food and Agriculture (2020), despite there being a significant focus on the water usage in cannabis growing from regulators and the public, the crop still represents the tiniest fraction of agriculture in the northern part of the state. It falls well below common feed crops like hay and oats, grapes, olives and apples. Most farms are about a quarter of an acre, says Grantham, which is small enough to exist discreetly, away from regulators’ eyes. The illicit cannabis grows fuel demand from lucrative overseas markets and remain difficult to regulate, although, according to recent reports, there have been millions of dollars confiscated and dozens of arrests made in more remote areas.
With so much undocumented, unregulated—but small acreage—cannabis planted throughout the state, the ag industry is left wondering: How much water are these farmers really using?
Grantham and his team studied just that, observing several permitted cannabis farms’ groundwater usage in the Emerald Triangle (Mendocino, Trinity and Humboldt Counties) and eleven other counties throughout Northern California that support growing cannabis.
The study found that, although California enacted The Sustainable Groundwater Management Act (SGMA) in 2014, which is designed to prevent “overdraft of groundwater and protect water quality and supplies for agriculture, residents, fish and other wildlife,” most cannabis grows are not on valley floors but on hillsides and tucked into more remote areas.
“Most of the cannabis farms fall outside of the groundwater basins regulated under SGMA, so well-use represents an important, but largely unregulated threat to streams in the region,” says Grantham. While the SGMA guidelines prohibit irrigation during dry months and encourage water storage from resources collected during wetter months, the cost and management of storage tanks or irrigation ponds has driven cannabis growers to seek wells providing groundwater.
Grantham points out there is no evidence that cannabis is a “thirsty” plant. In reality, weed uses about as much water as tomatoes, more than grapes and some other crops, but is not the water scourge some analysts have suggested.
Relying on data from legal grows, the Berkeley researchers found that “well use by cannabis farms is common statewide exceeding 75 percent among farms that have permits to grow in nine of the eleven top cannabis-producing counties….Farms growing larger acreages of cannabis pumped more groundwater for irrigation, while farms with on-farm streams or located in areas that receive more rainfall were less reliant on wells.”
Wells are not illegal and there are no rules about using groundwater for irrigation, but the fact remains that water resources are limited. The study also reports that wells drilled close to streams and rivers have the potential of diverting water from healthy streams. “Pumping from a well that is often connected to neighboring streams and rivers can affect upland watersheds and the environment in general,” says Grantham.
Although not discussed in the study, Grantham comments that so-called “trespass grows,” or growing on trespassed land, is also harmful to the environment because of the “nasty chemicals used, insecticide, and rodenticides that get into the food chain. Water quality has not been quantified yet.”
He also notes that “research is in its infancy and regulators have just begun to address these water issues. The handful of studies that have been done show a limited risk from permitted cannabis farms.”
But, the cannabis industry remains largely without oversight because of the large number of still-illegal, unknown plantings. Further research—and possible intervention—is unquestionably part of the future legislative landscape.
—Barbara Barrielle
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