Chem Tales: Science loses to arguing over cannabis's water use

How many cannabis plants would this water stash feed? Depends on who you believe.

This summer has been busy for law enforcement in California's Emerald Triangle, the sparsely populated rural counties where as much as 70 percent of the cannabis smoked in America is grown.

Large raids in Humboldt, Mendocino, and Trinity counties have yielded few arrests — a cop convoy is not subtle and provided outlaw growers enough advance warning to flee, and at least one search warrant was served at a grow that was legal — but have turned up tens of thousands of plants, worth tens of millions of dollars, plus one startling find.

At a grow site in the remote Island Mountain area, sheriff's deputies discovered a football field-sized water bladder. Whether pulled from a now-dry creek or a spring, that's the kind of sight that fuels outrage in the fourth long, hot summer of California's historic drought.

The Island Mountain raid hit private land rather than the national forest, meaning it didn't hit the loathed trespass or “cartel grows.” This was by design.

Raids are no longer staged based on mere plant counts. These days, an illegally-dug pond or poorly-built road is riskier for a marijuana grower than an extra row of plants. In a thematic shift, law enforcement is using environmental degradation as the reason for sending in the helicopters.

They're also using bad science.

The state Department of Fish and Wildlife is the lead agency on some of these raids. According to the DFW, a cannabis plant uses between 5 and 10 gallons of water a day. That's a wide range, based on a back-of-the-envelope estimate which has become fact.

These numbers aren't derived from a scientific study but from a single source who now repudiates the figure. In 2010, the Humboldt Growers Association, a legal cannabis farmers' advocacy group, first published the 5-to-10 gallon figure during Humboldt County's brief (and abandoned) effort to regulate outdoor growing. This year, Emerald Growers Association, HGA's successor, has steadily backpedaled from the 5-to-10 gallon estimate. That's a “worst case scenario” that was never intended to represent an average, says Hezekiah Allen, the organization's co-founder and executive director.

The problem is that that figure has since been published in a string of scientific articles, including this month's issue of Bioscience.

“This isn't science. It was a guess,” says Allen. “They're now taking that number and plastering it in the headlines, out of context.”

And so far, the state's environmental scientists have stood firm.

“These are the numbers [DFW] uses and will continue to use,” said Scott Bauer, a senior environmental scientist with the agency and one of the co-authors of the Bioscience article, in comments to the Sacramento Bee.

So how much water does a cannabis plant really use? The answer is that it depends. Which means the real answer, from a data-driven standpoint, is that nobody knows.

And now both the cannabis industry and the state's environmental stewards are pointing at each other and demanding a better-grounded figure. In the meantime, both the drought and enormous amounts of cannabis cultivation continue.

The cannabis trade is full of huge numbers. Medical marijuana sales top $1 billion in California. Legal cannabis sales exceed $2.7 billion nationwide. Wholsesale, marijuana is a $16.7 billion cash crop, almost double the California's wine industry.

All of these numbers are estimates. You can thank cannabis prohibition for that. As with all wars, truth — or at least reliable data — was an early casualty of the drug war.

To date, there has been no comprehensive study of how much water a modern, commercially-grown cannabis plant uses.

How much water a cannabis plant uses depends not only on its size but also on how it's grown. Many of the plants seized during the Island Mountain raid were in one-gallon pots, Allen says. These, clearly, cannot use five gallons of water day. However, large plants that yield five pounds of cannabis or more at harvest could easily use ten gallons a day. (A better way to calculate water usage may be by yield; the industry says a pound of pot needs one gallon a day over an 150-day growing season.)

In an email to SF Weekly, Bauer says that a wide-ranging study is needed. Enterprising graduate students may take notice, but they may also be disappointed. Marijuana is an unregulated industry. Good luck getting grants from the government or enough growers to produce a peer-reviewed study.

“We all want better science on this,” agrees Jeanette Howard, who heads the Nature Conservancy's water program and co-authored the Bioscience article. But for now, she says, “relying on the growers and what's been published in the past is the best we can do.”

The industry points right back at the scientists. Agencies like DFW “have a mandate, and the mandate says to use science to protect the wildlife of the state,” Allen says. “So give us a number, guys.'

What shouldn't be lost in all this is the premise of the Bioscience article: that cannabis production has an environmental toll. Nobody knows what the precise toll is, but that hasn't stopped people from guessing — or having those guesses accepted as gospel.

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