California Facing 'Invisible Water Surcharge'

Crop water demand in California's San Joaquin Valley has increased to the size of a major reservoir in just 12 years due to climate change, a study has found.

An integral region for agriculture, particularly in fruit and nut production, it has been subjected in the past 10 years to severe drought conditions, with extreme temperatures that have evaporated water supply.

Researchers of the new study, published in PLOS One journal, looked at climate data and crop measurements to estimate the overall water demand for the crops in the past 40 years, focusing on climate change based effects.

They found that an increase in the demand explains a great deal of "half of the cumulative deficits of the agricultural water balance" since 1980. This has meant there is more demand while groundwater supplies are still depleting. The researchers dubbed this "climate-induced increased crop water demand an invisible water surcharge."

"Scientists have long been concerned about the impact of climate warming on our planet's ability to feed a growing human population, as it impacts a number of important feedbacks between plant phenology or timing of crops, their pollination, length of growing season, and maturation," Joshua Viers, Professor of Environmental Engineering at the University of California, Merced, and study author told Newsweek.

"The swings in extreme precipitation—either too much or not enough—are exacerbated by this invisible surcharge, as a warmer, thirstier atmosphere will further stress a region that provides 50% of America's produce, including two-thirds of its fruits and nuts. Nine of the top 10 US agricultural-producing counties by revenue are in California, so it is definitely a concern for the region's economy and for the grocery basket of most Americans."

In the past 10 years, the researchers found that the invisible water surcharge increased crop water demand in the valley by 4.4 percent between 1980 to 2011. That is more than 800 gallons a year, which equates to the amount of water in a large reservoir, the study reported.

"While it is clear that the atmosphere has warmed, the measurable break to a new, warmer regime impacting agriculture across both wet and dry cycles is eye-catching," Viers said. "This isn't a gradual phenomenon, but rather an upward regime shift in evapotranspirative demand. In other words, there is a thirstier atmosphere due to increased warming and, that from an energy balance perspective, more water is transferred from soil and plants back into the atmosphere."

California has seen an increase in atmospheric rivers—concentrated corridors of tropical moisture that travel through the atmosphere—recently, which has increased precipitation in the state as a whole. In fact, the San Joaquin Valley recently saw the reemergence of Tulare Lake, which only forms when the lands floods, due to an excess in water.

However, it does not mean groundwater supplies are bouncing back quickly enough for the increased crop demand.

"For the water-scarce regions of the western U.S., the tug between supply—often not enough—and demand—ever-increasing with the growth of cities—is omnipresent. Technological breakthroughs that might augment supply, such as desalination, have promise but have a price point that is approximately 30 times higher than most farmers pay for surface water," Viers said.

Of finding a solution to the issue, he added: "Using groundwater more strategically will be critical, and that will require that we manage our aquifers more efficiently, creating opportunities for recharge during the exceptional wet years, like the one California experienced a year ago. It will also require some strategic changes in cropping, such as seasonal fallowing of some crops.

"Ultimately, it is an all-the-above strategy that will be needed that balances all the water demands with a highly variable supply, and now an increased demand from the atmosphere."