During a winter of blizzards, floods, and drought-ending downpours, it’s easy to forget that California suffers from chronic water shortages—the long-term decline in the state’s total available freshwater. The flooding this rainy season is not going to change that.
How is this possible, given the relentless series of atmospheric river systems that have dumped near-record snowfall over the Sierra and restocked the state’s reservoirs?
It’s about groundwater.
California uses more water each year, most of it for food production, than is supplied by renewable sources like rain and snowfall, even in the wettest winters like this one. The gap is filled by groundwater, which for a century has sustained California’s water resources, particularly during droughts, when it provides 60 percent or more of irrigation water supply for agriculture.
But groundwater can be renewed slowly, to the extent that it can be renewed.
The long-term disappearance of groundwater is the primary factor behind the steady decline in total available freshwater in the state, which hydrologists define as snowpack, surface water, soil moisture, and groundwater combined.
Although this winter will match or exceed the precipitation totals of the wettest winters on record (1968-69; 1982-83), like those winters, this one will do little to stop groundwater depletion. The gains made during the wet years simply cannot make up for the excess pumping during the intervening dry years. In fact, the state’s groundwater deficit is now so great that it will never be fully replenished.
In November, measurements from NASA satellites showed that California’s total freshwater levels had reached a 20-year low, likely the lowest ever recorded for the state. Since 1961, 93 million acre-feet of groundwater have disappeared in the Central Valley, equal to 3.4 times the volume of Lake Mead at capacity. Since the 1860s, an estimated 142 million acre-feet has been depleted.
In 2014, California finally passed the Sustainable Groundwater Management Act, or SGMA, its first regulation governing groundwater pumping. The law it offers the opportunity to define a path towards groundwater sustainability, if not recovery. However, its slow implementation and the lack of quantitative targets threaten to undermine its potential.
Under the law, local groundwater sustainability agencies were formed to manage the state’s depleted groundwater basins. Basin by basin, agencies must develop and implement sustainability plans and have them evaluated by the California Department of Water Resources. The law sets 2042 as the goal to achieve overall sustainability.
Yet to date, the state has fully endorsed only 12 of 94 watershed plans, and just this month found plans submitted for much of the San Joaquin Valley inadequate to deal with the “critical overdraft” of groundwater in the region.
SGMA’s faltering pace calls into question whether California can realistically meet its goal of full compliance in two decades. In fact, the long timeline is already having profoundly negative consequences.
In December, my research team released a report showing that groundwater depletion in California’s Central Valley accelerated during the megadrought years between 2019 and 2021, rather than slowing with the implementation of sustainability plans and rules. . In those years, Central Valley groundwater disappeared at almost five times the long-term average depletion rate.
The finding initially caught our research group off guard, but it was confirmed by ground-based observations of water levels and a record number of groundwater wells going dry. In hindsight, we shouldn’t have been surprised. The specter of SGMA limits on groundwater use likely sparked a rush to drill more agricultural wells, to plant more thirsty nut trees and of course, to pump more groundwater.
In the midst of this winter’s atmospheric rivers, Governor Gavin Newsom ordered 600,000 acre-feet of the state’s abnormally high river flows diverted to recharge and store groundwater in the Central Valley. Along with other supply-side efforts, including Newsom’s decision last year increase annual groundwater recharge by at least 500,000 acre-feet per year, that move could reduce current groundwater depletion rates by up to 25%.
But such orders will not guarantee the future safety of California’s water. That directly depends on the timely and successful implementation of the Sustainable Groundwater Management Law.
To accelerate groundwater sustainability, the state must dedicate additional resources to its assessment and monitoring effort.
Beyond that, California should supplement the Sustainable Groundwater Management Act in three ways.
First, you must order a comprehensive assessment of the volume of freshwater available in the state, how its quality and accessibility varies, what is renewable versus nonrenewable, and the environmental and human effects of pumping it. It is shocking that this fundamental information is not widely known today.
The state also needs to be more transparent about what underlies its standards for sustainability plans and recharge projects. California should have specific goals to reduce and halt groundwater depletion, just as it has for use of fossil fuels and carbon dioxide emissions.
Is the current average depletion rate in the Central Valley, around 2 million acre-feet per year, the goal? To understand and plan for the future, Californians need to know what level of groundwater will be maintained and how both recharge efforts and reduced pumping will be used to achieve that level.
Finally, industry, particularly agriculture, must account for its use of water. SGMA’s sustainability agencies are required to track overall water use; individual farms and ranches may not be. But California cannot achieve water security without a deep commitment to stewardship by industry, and the stewardship requires that water use be routinely measured and reported.
Groundwater, even in its depleted state, is California’s most valuable water resource, and the Sustainable Groundwater Management Act is the state’s only hope to protect it. If the law fails, it would be catastrophic.
California must commit to doing everything in its power to ensure your success.
Jay Famiglietti is a professor of global futures at Arizona State University. He is the former Senior Water Scientist at NASA’s Jet Propulsion Laboratory and a former member of the California Regional Water Boards in Santa Ana and Los Angeles.