California agriculture has experienced just about every form of climate change-induced calamity: Heat, drought, fire, floods. None bodes well for the future of farming in this state that is the U.S. king of agriculture.

But there are a couple of less headline-worthy factors that may determine what crops will survive if climate change trends don’t at least slow down. One is the state’s winters – yes, winters – and the other is its management of groundwater.

Challenges ahead for sure. In the end, however, there for some is optimism that the California agriculture communities’ ability to continue adapting gives reasons for hope.

The importance of ‘chill hours’ for key crops

“Wintertime lows have gotten warmer,” says Dan Sumner, the Frank H. Buck, Jr. Distinguished Professor of Agricultural and Resource Economics at the University of California, Davis and a California farming region native. “We all talk about it in the middle of the summertime because it’s hot outside, but the real news is the wintertime lows.”

The reason? Perennial crops, comprising the bulk of California’s top farm commodities, need off-season dormancy to regenerate, so temperatures must remain below a certain threshold for at least a minimum amount of time. That concept is called “chill hours.” It’s crop-specific, and the fruits and nuts that are among the bedrocks of California agriculture are the ones most needing the right number of chill hours. Otherwise fewer buds, smaller fruits, lower yields.

According to the most recent census data from the U.S. Department of Agriculture, California still provides more agricultural product than any other state, accounting for 11% of the national total.  That output includes more than two-thirds of the nation’s fruits and nuts and more than one-third of the nation’s vegetables.

California’s top 10 agricultural commodities among its more than 400 in order are: dairy products, almonds, grapes, pistachios, cattle, lettuce, strawberries, tomatoes (largely for processing), floriculture, and walnuts.

Those are largely perennials needing their chill hours to make them as productive as they need to be, and therefore worth growing. Crops such as nut trees and grapes are large investments, so low yields may make them money losers.

Crop diversification to diffuse risks

A 2018 publication – “Climate Change Trends and Impacts on California Agriculture: A Detailed Review” – provides an overview of the prevailing research around temperature, precipitation, and other factors and how they are likely to affect the state’s agriculture over time.

The report, led by University of California Merced climate change extension specialist Tapan Pathak, indicates that higher minimum and maximum temperatures are resulting in lower numbers of chill-hours.

The authors of that study say that by around 1950 “growers in the Central Valley could rely on having between 700 and 1,200 chilling hours, depending on the location of their orchard.” But currently, they say, for crops requiring more than 700 hours – apricot, kiwifruit, peach, nectarine, plum, and walnut – only between one-quarter to one-half of the valley is suitable. By 2080-2095, they project, only about 10% of the valley will remain viable for those crops.

Fruits such as apples, cherries, and pears needing chill hours of at least 1,000 hours were already barely suited to Central Valley conditions 20 years ago, according to the publication.

Perennial crops also make agricultural systems less flexible and therefore less able to deal with whatever climate change throws at them. Annual crops, on the other hand, can be changed year-to-year to accommodate climatic changes.

“You really don’t want to miss a year,” says Nathan Mueller, an assistant professor of ecosystems science and sustainability and soil and crop sciences at Colorado State University. “Diversification in general is going to help diffuse that risk,” says Mueller, who studies world-wide climate risk agricultural trends,

And, he says, it all intersects with water. Not having enough makes everything worse.

Striving for balance in the water/heat dance

Drought and heat exacerbate themselves and each other. When it’s hot, whatever precipitation there is evaporates faster, often not making it into the soil to become groundwater. The warming climate also likely means precipitation will come in the form of rain rather than snow, even high up in the Sierras so crucial to California’s water supply.

The result can be a smaller snowpack, which in turn means that what Mueller calls a “free giant reservoir” will melt earlier and at higher elevations than long has been the case. So there will be less of that gradual melting that in “normal” years constantly re-supplies surface and groundwater without wasting too much of those resources.

Add to the equation that heat spells, now more frequent than previously in winter months, can result in more off-season melting. Furthermore, extended dry conditions may mean that when it does rain, the water may simply run off hard-packed soils without helping parched crops or soaking into groundwater supplies.

So essentially, the drier it gets, the drier it continues to get.

“It means the waters largely are going out the Golden Gate without even doing the ecology very much good,” Sumner says, referring to the situation around the San Francisco Bay area. “If it’s warmer in the summer like it was this year, hotter and drier, then you have less water to start with for your irrigation and greater demands for irrigation in terms of the climate.”

In effect, it becomes a cycle, an endless loop, “and that becomes quite severe,” Sumner says.

Another critical issue: California agriculture mainly relies on irrigation. About 80% of human water consumption in the state goes to agriculture, leaving the remaining 20% for residential, industrial, and other uses.

When groundwater use is not metered or priced, guess what happens

On top of that, in California most agricultural groundwater is not priced, while residential is. Agricultural operations have to pay for only the costs to extract the groundwater, not for the water itself.

Groundwater also isn’t metered, so it’s unclear how much farms are using, but it’s estimated that groundwater makes up about 40% of farm use in what used to be considered an average year, meaning a year with less intense drought. In a drought year, that farm use share can jump to about 80%.

But the outlook now is likely on the verge of changing, as the California Sustainable Groundwater Management Act, passed in 2014, is about to go into effect. It requires the development and implementation of locally based groundwater sustainability plans to prevent overuse of groundwater.

Katrina Jessoe, an associate professor in the department of agricultural and resource economics and the associate director of the Center for Watershed Sciences at UC Davis, and Ellen Bruno, an assistant cooperative extension specialist at UC Berkeley, think they know what’s going to happen on the agricultural front if farmers have to start paying for groundwater.

They’ve been looking at agricultural water use in some areas that had already been charging for groundwater, such as the Pajaro Valley along the central coast. There they were able to look at both changes in water use and agricultural land use.

Pajaro has had pricing and metering since 1994, with a price increase in 2010 – so Jessoe and Bruno could look at actual changes over 10 years.

They say farmers responded immediately to the price increase by reducing production of “lower value crops.” In years two to five they found that farmers beginning to retire agricultural land or temporarily take it out of use. At first, the farmers’ actions were driven by a reduction in use of fallowed land, they say. But over time, especially after five years, they found farmers also reducing their irrigated acreage.  

“We’re going to see a contraction of agricultural land, a reduction in the acreage of agricultural land, a reduction in farm size as measured by acreage,” says Jessoe. “It could be a preview of how water scarcity or reduction impacts agricultural land use in California.”

But just what constitutes a “lower value crop” is a little hard to know.

Bruno suggests it’s a combination of how much water is required and the economics of various crops. “We’re assuming that farmers are optimizing and that the switch we’re seeing due to the increase in price is a switch to the crops that give you the most bang for your buck now that water’s more expensive,” she says.

At end of day, hope for adaptation … and no ‘nightmare’

“California grows such a diversity of crops, it’s hard to even think of a staple having a huge disproportionate impact that ripples through the system,” Bruno says. “We’re not talking about millions and millions of acres of corn and soybeans all being hit the same way.”

In the end, she and others don’t see a nightmare scenario despite the burned and plowed-under crops from fire, heat, and drought this summer.

“It undersells the adaptive capacity for agriculture,” she says. “That might be true if we couldn’t adapt to anything, but we constantly find ways to adjust both through policies and farm level changes and technological advances.”

Jan Ellen Spiegel

Jan Ellen Spiegel is a long-time Connecticut-based journalist whose career has included radio, television, print, and digital reporting. She has won awards for her reporting on energy, environment, climate...