What Is Drought? You May Think You Know But You Probably Don’t

A powerful series of atmospheric river storms pounded California in the first months of 2023, drenching large regions of the state with more rainfall than they normally receive in a full year. Downtown San Francisco, for example, was hit with 26.3 inches of rain by March 6, 2023. That was 115 percent of a normal full year of rain, according to Golden Gate Weather Service. At Oakland Airport, the 24.78 inches were 133 percent of normal for a year.

Southern California was soaked as thoroughly as the northern part of the state. Downtown Los Angeles received 142 percent of its normal year’s worth of rain while Burbank-Bob Hope Airport was pelted with 152 percent of a normal year.

Before the 2023 rains came, California was deep in a drought that, depending on how it was measured, lasted as long as 23 years. According to a study by researchers at UCLA and Columbia University, it was the driest period to afflict the North American West in 1,200 years.

As the rains fell, was the great drought, and California’s seemingly endless water crisis, finally over once and for all?

What Is a Drought, Anyway?

To figure out whether the 2023 storms ended the California drought, it helps to understand exactly what a drought is. And that definition is not as simple as it might appear. 

The National Drought Mitigation Center at the University of Nebraska defines drought as “​​a deficiency of precipitation over an extended period of time (usually a season or more), resulting in a water shortage.” Seems straightforward enough, though the definition offered by California’s Department of Water Resources is more nuanced.

“Defining drought is based on impacts to water users. California is a big state and impacts vary with location,” the Department says on its website. Hydrologic conditions causing impacts for water users in one location may not represent drought for water users in a different part of California, or for users with a different water supply.”

The state also emphasizes that drought is a “gradual phenomenon” that can be felt only over an extended time. Even when rainfall dries up over a given year, not all of California will experience drought conditions, because the state’s “extensive system of water infrastructure and groundwater resources” keep water flowing.

Glen MacDonald, a UCLA distinguished professor of geography who specializes in climate research, wrote that California’s “historic” drought was not even necessarily due to a shortage of precipitation. Writing for the online journal Yale Environment 360 in 2015—in the midst of California’s devastating drought of 2012 through 2016—MacDonald said that there were three main factors creating what he called the “perfect drought.”

Those factors were excessive heat, increasing depletion of groundwater, and water shortages in the Colorado River, which supplies about one-third of the water consumed by Southern California municipalities. Agriculture in Riverside and Imperial counties also depends on water from the Colorado River and its two main reservoirs: Lake Mead—located in Nevada and Arizona behind the Hoover Dam—and Lake Powell, in Utah and Nevada.

Mead and Powell are the country’s largest and second-largest reservoirs, respectively. They have fallen to record-low levels over the course of the west’s 23-year “megadrought,” with Lake Mead sitting about 70 percent empty, and Powell even worse, almost 80 percent down from its capacity.  The reservoirs were nearly full at the turn of the 21st century, and the 2023 rains did little to raise their levels. Climate scientists say that there’s no way they will refill anytime in the foreseeable future, mainly due to sharply increased demand for their water.

Does Climate Change Cause Drought?

According to MacDonald, California’s low rain and snowfall totals over the course of the drought cannot be ascribed to human-driven climate change. While the amount of rainfall and snow varied, it rarely left the “boundaries of natural variability,” and based on historical records even the low precipitation levels were never “exceptional.”

What can, in fact, be ascribed to human-caused climate change are rising temperatures. California suffered through record-setting heat waves in 2014 and again in 2022. 

A report issued in November 2022 by the state’s Office of Environmental Health Hazard Assessment found that the state’s average annual air temperature has risen by 2.5 degrees since 1895, with the fastest rate of increase starting in the 1980s. The decade from 2012 to 2022 saw eight of the 10 hottest years ever recorded since California started recording temperatures.

The hotter the air, the faster water evaporates—including water stored in reservoirs, which then become depleted as their water turns into gas and floats into the sky rather than remaining on the planet’s surface where people can drink it, bathe in it and so on. 

Hotter air temperatures also cause precipitation to fall as rain rather than snow. That phenomenon results in a thinner snowpack. What is snowpack? As the term implies, it's the vast amount of snow that accumulates high in the mountains. In California, most of the snowpack builds up in the Sierra Nevada mountain range. During spring and summer months, the snow replenishes rivers, reservoirs and groundwater tables.

The state typically draws 30 percent of its water supply from the Sierra snowpack. Because California doesn’t see significant precipitation in the spring and summer, even in relatively wet years, the snowpack serves as an essential way to bank water for the dry months.

Due to the rising temperatures driven by human-caused climate change, the snowpack has been shrinking since the start of the 20th century and could be depleted by 75 percent of current levels by the end of the 21st, according to the Natural Resources Defense Council.

Underground Water Supplies, Drought and Climate Change

As reliant as California is upon water from high in the mountains, the state depends even more heavily on water naturally stored under the Earth’s surface. According to the California Department of Water Resources, the water that lies beneath our feet provides 38 percent of all water consumed in California during an average year. That’s pretty typical of regions around the world. Globally, about one-third of all water use is drawn from groundwater. In especially dry years, almost half of California’s water (46 percent) comes from groundwater basins.

Underground basins, at least potentially, are California’s greatest water storage mechanism, with the capacity to hold up to 12 times more water than the state’s entire reservoir system.

California’s groundwater is low. Very low. That’s not necessarily the fault of climate change, but rather another human factor—pumping. In the San Joaquin Valley and many other agricultural regions, farmers have “overdrafted” groundwater basins—that is, pumped too much water out. 

In rural areas, homes are not generally connected to municipal water systems, so individuals and families depend on groundwater extracted via modest wells. In areas where agricultural businesses have overpumped groundwater in order to keep their crops growing, residential wells dry up and people are left with no water at all. They become victims of a drought that is largely caused by human activity.

How to build the underground water supply back up again? The primary means of recharge—that is, refilling the groundwater basins—is exactly what one might expect: rain. The melting snowpack also helps to recharge groundwater basins. Just as rising temperatures affect the snowpack, they also make refilling the groundwater supply more difficult.

Rain must filter through the surface soil to reach the underground basins, or “aquifers,” but higher temperatures cause surface water to evaporate more quickly and as a result, less of it seeps through.

Because drought is defined as a shortage of water, not simply a shortage of rain, climate change and overpumping of groundwater are primary culprits in perpetuating drought. According to a 2022 study by World Weather Attribution, a global scientific group, climate change has increased the likelihood of drought in the western United States and, for that matter, around the world, by a factor of 20.

Drought conditions like those that gripped California—as well as the northeastern United States, and even China—would occur only every 400 years under “normal” conditions. With human-caused climate change, droughts of that magnitude will occur every 20 years, according to the study.

So, Did the 2023 Rainstorms End the Drought?

There is no doubt that the voluminous rains of early 2023 improved California’s drought conditions significantly. As of March 2, the U.S. Drought Monitor at the University of Nebraska showed about half of the state (49.13 percent) under “moderate drought” and just 25 percent in “severe drought.” Compare that to three months earlier when 99.48 percent was experiencing moderate drought and 85 percent in severe drought. At that time, 41 percent was afflicted by “extreme drought” and 13 percent stricken by “exceptional drought.”

After the rainstorms, no area of California was listed as “extreme” or “exceptional.”

January of 2023 was the 13th wettest January in 129 years, according to the project’s Drought.gov website. If fact, even after just two months of rain, 2023 was the 13th wettest year of the past 129.

The wonderfully wet conditions, however, did not mean that California’s drought was at an end, climate experts warned.

“These storms…did not, nor will they fully, end the drought, at least not yet,” Yana Garcia, secretary of the California Environmental Protection Agency, told the Los Angeles Times. “We’re in better shape than we were two months ago, but we’re not out of the woods.”

“We would need five or six years at 150 percent snowpack to refill these reservoirs,” Colorado State University climate researcher Brad Udall told National Public Radio. “And that is extremely unlikely.”

Groundwater supplies remain low as well, and will also take years—if it ever happens. In some areas, such as the San Joaquin Valley, groundwater aquifers are located so deep below the surface that water takes months to drain through the soil to reach them.

Nor is recharging groundwater basins simply a matter of sitting back and waiting for rainfall to percolate down to the aquifers. The process requires planning on the part of state and local governments, as well as sacrifice from agricultural businesses, which must cut back on groundwater pumping to allow the underground supply to refill.

Water must be captured, piped and pumped to specific locations, or else much of it simply runs off and ends up in the ocean. In California, according to an analysis by The New York Times, lurching bureaucratic machinery, insufficient infrastructure, and complex water-rights arrangements that go back decades prevented the state from taking advantage of the heavy rains, at least when it came to refilling groundwater basins.

The continuing drought even after a season of history-making storms represents yet another missed opportunity for California to end its water misery, experts told the Times.

“We can’t miss it anymore. We just can’t,” Matt Hurley, a Groundwater Sustainability Agency official in the McMullin Area, outside of Fresno, told the paper. “Too many people’s lives and treasure are at stake.”