Last summer, I found myself standing among the wind-whipped peaks of Southern California’s San Bernardino Mountains, scanning a rocky canyon slot for signs of water. There weren’t any. “It looks like it hasn’t run here in a while,” wild-trout biologist Jennifer Hemmert said of this small headwater of the Santa Ana River, kicking at the thick pine duff right in front of a large rock, a former prime trout lie. The summer of 2022, like most of the 10 consecutive summers before it, had been historically dry. A former streambed ecosystem, a vein of life-bringing water, had dried into something with the consistency underfoot of potpourri. Farther downslope, a wildfire had turned giant cedars into matchsticks.
I and several volunteers from the Fisheries Resources Volunteers Corps, a local organization of anglers and outdoors enthusiasts, had planned to help out as Hemmert and other field biologists used electrofishing equipment to study and catalog wild-trout populations in Heart Bar and Coon Creeks. Studies conducted 17 years ago had showed these creeks flowing consistently and holding wild trout. But when Hemmert ventured into a former stand of willows that had shaded the stream, vegetation now dead and dry as a bone, all she found was an angry rattlesnake and mud where a spring once had flowed. “I’d say this spring has dried due to extended drought conditions,” said Russell Marlow, a California Trout senior project manager and fellow stream ecologist.
This “field truthing,” checking out what actually was going on, was being done to compare the creek with a model created by Hemmert and her colleagues at the California Department of Fish and Wildlife alongside CalTrout. Using historical flow readings and information about slope, tree cover, precipitation patterns, and more, it predicted a number of headwaters that should still have water and hold wild trout. This one didn’t. Both Heart Bar and Coon Creeks are part of a hydrological system. When rain or snow falls in areas with specific “spongy” geological formations, water is quickly absorbed into the spaces between the rock. This formation is known as an aquifer. Then, a mixture of gravity and geology forces this water — groundwater — to the surface, forming a spring. For California’s wild trout and other species, the streams these springs feed are vital habitat. But when Hemmert and the volunteers “field truthed” Heart Bar, Coon, and eight other promising blue lines in the San Bernardinos in 2022, they found flows were lower than expected or nonexistent at every single one.
That changed in January, February, and March of 2023 as consecutive “atmospheric river” storms dropped heavy rains and snow across California. From Los Angeles, I could see snow on the Transverse Range; residents in the San Bernardinos were socked in. The snowpack rebounded to historic levels, then was partially melted by rain, causing widespread flooding and muddy, blown-out rivers. The historically wet winter has visibly boosted water levels in creeks, rivers, and reservoirs across the state. Now, several months later, it’s clear that in many definable ways, California’s recent drought is largely over. But anglers would be wrong to think the state’s water crisis is cured after one wet winter. California’s last decade was marked by long periods of hot, dry weather, accentuated by short, intense rain periods. Unfortunately for the aquifers across the state that feed many important rivers, “one or two very wet years cannot replenish the aquifer quickly,” said Jean Moran, a professor of hydrogeology at Cal State East Bay. She and other hydrogeologists I spoke with worry that California’s succession of winter storm systems might be another example of long stretches of extreme heat and dry weather accentuated by occasional, intense, monsoon-style rains.
These extreme weather patterns are proving very hard on trout and on the fragile stream ecosystems that support them. As Jay Lund and Andrew Rypel, two UC Davis water scientists, recently wrote on a California WaterBlog post titled “The Drought Is Dead. Long Live the Drought,” “The lack of water for ecosystems and a deluge of other impacts is generating a ‘stair-step’ shape of ecological decline over time, whereby stocks of native species exit the drought in worse condition than when they entered.”
This means there is still a problem on the horizon for the many trout that rely on California’s acquifers. Whether 2023’s wet spring is a brief respite from the drought or the beginning of its end, ecosystems and trout have been deeply affected by recent dry weather.
After the rains fell, I was reminded of something Hemmert told me back in 2022 as we hiked up that dry gulch in the San Bernardinos. “We’ve been sitting in multiple periods of extended drought,” she’d said. “When there has been a wet year, you’re never really getting enough to replenish what has been lost from a previous multiyear drought.”
One hopes that the current state of these life-giving aquifers will mark a low point in the condition of California’s hydrological systems. Otherwise, the drought conditions of 2022 could be a preview for what future decades of climate variability bring to our rivers.
Where the Water Is
Much of the flow in California’s rivers is generated by snowmelt and run-off, but a number of its most important wild-trout rivers depend on water from groundwaterfed springs. As the state’s rivers and the reservoirs that impound them have refilled, it’s tempting to breathe a sigh of relief, but the water you can see isn’t the only water that matters.
What matters just as much is what’s beneath the ground. Scientists have classified more than five hundred different “groundwater basins” across the state; of those, 127 basins provide 95 percent of the state’s annual pumping of groundwater. They estimate these aquifers alone can hold 8 to 12 times as much water as all of the state’s reservoirs combined.
“Aquifers offer a much, much larger volume for water storage than surface reservoirs, but it’s not possible to fill that volume quickly, and especially not with just one year of very high precipitation,” says Moran. “Although 2023 will be a good year for recharge, most of the aquifer recharge water will end up evaporating or sublimating (sometimes, after being taken up by plants and trees) or running off into reservoirs or the ocean. In less stressed regions, including mountain areas where groundwater discharge is via springs and late-season baseflow in streams, the good recharge year could temporarily reverse (or at least slow) the downward trend in discharge, but it will not f ill the large subsurface reservoirs that moderate interannual variability.” In short, says Moran, “Groundwater is not a sustainable resource unless loss is balanced by recharge.” Especially on some smaller aquifers, she said, “there were clearly some effects” from the drought. “And those effects are important for the streams, springs, and fish connected to the aquifer.”
Today, scientists can use techniques such as isotope tracing to study how “old” the water in an aquifer is — how long the water has been underground. In the United States and across the world, some massive aquifers hold water that’s been there for hundreds of thousands or even millions of years. In California, though, water ages tend to be relatively “young”: geology, topography, water management, and climate create a large range in water ages, with groundwater that can spend as long as a thousand years or as little as a few weeks underground before reemerging as a spring — cold and clean, and important for trout looking to survive drought and high temperatures. And an aquifer that holds young water — say, seven or eight years — is more susceptible to long-lasting drought conditions. That’s what we were seeing in the San Bernardinos in 2022. Watchers of aquifer-fed springs across the state also saw issues much like the ones I witnessed there. “Even the big springs are having reduced flow during these longer droughts,” Carson Jeffres, the field and lab director for the Center for Watershed Sciences at UC Davis, told me.
The Elephant in the Room
A warmer planet has exacerbated California’s drought, but it hasn’t necessarily meant less precipitation. Instead, after long stretches of hot, dry conditions, the same amount of precipitation as in past years falls in a more concentrated pattern. During these periods of climate “whiplash,” wildfires decimate watersheds. Hotter days after heavy snowfall and rain-on-snow events cause mass melting, which brings floods. During intense rain events less water is absorbed into the ground, and torched hillsides erode into streams.
In 2022, the effects of the drought hit close to home for me. Until recently, the East and West Forks of the San Gabriel River, which originate in the San Gabriel Mountains east of Los Angeles, were healthy ecosystems for trout. Although by 2020 California’s drought had reduced their flows, during the pandemic, plenty of good f ishing could be found in the leafy, shadowy, sycamore-filled canyons. Then, in October and November of 2020, the Bobcat Fire burned through 115,000 acres, devastating the watershed. John O’Brien, a California state fisheries biologist who has worked in the San Gabriels for the past 20 years, has seen drastic changes since the fire.
“The elephant in the room is the changing climate,” said O’Brien. “I see it as a one-two-three punch. The first punch is prolonged and extensive drought.” In the early 2000s, the East Fork typically ran 10 to 20 feet wide in the summer, with pools from 4 to 6 feet deep in places. After the prolonged drought from 2012 to 2017, O’Brien told me, the average width of the stream decreased to less than half of that, and the pool depth diminished.
“Heat waves — they’ve been prolonged and extensive, which causes quite a bit of evaporation and drawback in flow,” O’Brien said. “The main thing was the amount of rainfall and snowfall. The water from rain percolates into the aquifer, recharging the streams over time.” The smaller, younger aquifers in the San Gabriels, much like their cousins in the San Bernardinos, appeared affected by precipitation changes and hotter temperatures, even before the second punch: wildfire.
The Bobcat Fire burned the riparian canopy in the canyons of the West Fork that kept the river shady and cool in the summer. Then came the third punch, summer monsoon rains. They filled the streambed with sediment. This caused a loss of invertebrate life, with a cascading effect on the ecosystem. On the upper East Fork, the gravel became cemented into the streambed in what biologists call a “tufa” layer. The filled-in pools provide little spawning habitat for trout.
The rains and snow in the spring of 2023 brought high runoff. That’s helped cut out deeper refuge spots trout need in the summer. But the same runoff that flushes out debris, sediment, and silt can also scour the bedload, causing loss of spawning gravels. Given another wet year, O’Brien said, trout populations in the watershed likely would improve. But for now, tough conditions persist. “Drought, fire, monsoon,” O’Brien said. “One-two-three. An almost complete knockout punch.”
Groundwater and Wild Trout
Native trout are often the most vulnerable to this knockout punch. A total of seven shallow headwaters streams in the Mount Shasta area still hold pure McCloud River “redband” trout. These native California fish once ranged throughout the mainstem McCloud River above Middle Falls and its tributaries and perhaps the lower river and its tributaries, as well. Today, redbands are designated a sensitive and rare species by regulatory agencies, in part because crossbreeding in most of the upper McCloud has essentially wiped out their pure genetics in those waters and elsewhere. Based on population estimates made during the 2014– 2015 drought, their entire population is likely around twenty-five hundred fish.
Sheepheaven and Ebson Creeks, two of the streams that still hold genetically pure redbands, are fed by springs via volcanic tube systems underneath Mount Shasta and run above ground for less than a mile before the water returns to the aquifer underground. They are windows that let us see how drought and climate change are affecting groundwater and wild trout in the region.
Michael Dege, who heads the CDFW’s Northern Region Heritage and Wild Trout Program, has been closely monitoring the creeks for over a decade. The beginning of this drought period, in the winter of 2013, hit both creeks particularly hard. “There was no precipitation at all,” Dege says. “Then a very cold spell in December froze some of the stream. Then flows dropped out underneath, so it was frozen pools with no water underneath. We found bodies of redbands scattered around.”
Trout and other salmonids are ectothermic — their body temperature is controlled by their environment. Increased temperatures can make life harder for them.
Further drought between 2014 and 2022 killed more fish. In the summer, flows at both creeks hover around 0.5 cubic feet per second. In extreme droughts, that drops to between 0.5 and 0.6 cfs per minute. The remaining wetted areas of both creeks continue to shrink. “It looks just like a rocky bed that is obviously a creek bed, but totally dry,” Dege said. “When I take people to look at it, they say, ‘You’re telling me there’s fish in there?’”
As the aquifer level dropped, both streams turned from flowing creeks into about a thousand feet of “wetted habitat,” areas where fish could still live. In the summer of 2022, both creeks began experiencing water-quality issues, killing more fish. “This didn’t happen in 2014 or 2015,” Dege said. “At some point, we’re very susceptible to losing the stream’s population.”
Heavy snowpack blocked Dege and his team from surveying the streams in April and May. He expects to check on them this summer. Until then, he won’t know the implications of this past winter’s storms.
Water Temperatures
Rivers f low downhill, and so can their temperatures. In the Cascades of Northern California, snow that falls on young volcanic systems melts, percolating into the groundwater system as a cooling recharge. In this region, when a stream passes over a fault line and this water springs up into its flow, it often creates an anomalously cool area where before the water had been warmed by the sun. Scientists note marked temperature drops where springs enter these river systems, and it’s clear that this colder, spring-fed water plays an important role in the ecosystem and in keeping its trout happy and healthy.
Groundwater temperatures thus provide a buffer against warmer climate, but springs are not necessarily eternally cold, and the temperature exchange can work in reverse, too. As a recent study of the springs that f low into the Fall River shows, warming temperatures on the earth’s surface can affect groundwater temperatures when water from the surface recharges the aquifer.
In the volcanic Medicine Lake highlands northeast of Mount Shasta, scientists from the US Geological Survey were able to model the effect of surface temperature change in spring complexes that host groundwater-dependent ecosystems. “In this basin,” states the paper, “upper basin groundwater temperatures are strongly affected only by recharge conditions.” And those conditions are warming. Global-warming scenarios developed by the UN Intergovernmental Panel on Climate Change predict an eventual temperature increase of more than 2.5 degrees Celsius, with warming above 1.5 degrees Celsius occurring by the mid-twenty-first century. Given a 1.5-degree Celsius increase in the earth’s surface temperature, which according to another recent study appears likely by the early 2030s, the Fall River springs paper models a 3-degree Celsius (5.8 degree Fahrenheit) increase in the average temperature of the recharged water over the span of the next 15 to 20 years.
What does that temperature increase mean? Trout and other salmonids are ectothermic — their body temperature is controlled by their environment. And although the paper found that “absolute temperatures within the example system do not exceed those required by many salmon and trout in the region,” increased temperatures do tend to make life harder for trout.
“Say the water is 12 degrees C now,” said Jason Dunham, a coauthor of the paper and a USGS supervisory research ecologist. “If water temperature increases up four degrees C, to 16 degrees, a trout will need to eat more to survive. And with plenty of food, they might be OK. But they’re also more at risk of pathogens. Once above the critical point of 18 degrees C water temperature, trout can very easily die for other reasons. In short, as water temperatures increase, trout have less and less room to be successful.” Such effects are likely magnified downstream as the distance from cold groundwater inputs increases and surface water temperatures increase.
Rising water temperatures from climate change is a big concern for trout in California. CalTrout’s recent SOS II: Fish In Hot Water report estimates that 45 percent of California’s salmonids could become extinct in the next 50 years, given current climate-change temperatureincrease scenarios. And it’s not just about slow, long increases in average water temperature. “Heat waves” in streams, during which extreme water temperatures are sustained over days, appear to be increasing. A recent study by researchers from UC Davis and elsewhere found that heat waves in streams and rivers had doubled on average, from 11 in 1995 to 25 in 2021.
Looking ahead, Dunham said, “the solid months of snow that we had this year and the overall snowpack will definitely help with recharge, but I would anticipate carryover effects from the preceding drought. If we get a few good years in a row then we might be on a track to some form of recovery. Also note that even if that occurs, it’s more likely that temperatures will be warmer than in the past.” “I wish I had better news,” said Dunham. “The aquifer is far more buffered against climate variability than surface water. But over time, even that will change.”
A New Study of California’s Springs
A study of springs has recently received more than $1.5 million in funding from the California Department of Fish and Wildlife. Called “Improving Drought Resilience for Water Supply and Native Fishes in the Upper Sacramento Basin: Groundwater Spring Sensitivity to Climate Change, Drought and their Contribution to Native Fish Life History,” it will focus on springs that feed the upper Sacramento, McCloud, Fall, and Rising Rivers, along with Hat Creek. CalTrout, UC Davis, CSU East Bay, Stanford, and Lawrence Livermore Laboratories are partnering on the study, which will identify which springs are most at risk from the effects of drought, gather other important data, and undertake community outreach.
— Chris Wright
