The current drought began when Kent Norman was just 2 years old. Farming is in his blood. His family has worked the land in Stockton, California, for generations. But the last two decades have created one of the most severe droughts in the region history: Over the course of his life, south-western North America has become drier than it has been in .
Megadrought in North America
This story is part of our Parched Earth series about the ongoing megadrought in south-western North America, the worst such drought in more than 1200 years
This year, the Normans’ water district didn’t receive its usual water allocations from the , a critical irrigation network that distributes water to 1.2 million hectares of farmland. Unable to irrigate with surface water, Norman says his family was comparatively lucky. They were allowed to pump water for their 590 hectares from existing wells. Still, the water table has declined to the extent that one of their wells recently ran dry. “As groundwater levels drop, we have to pay more and more for electricity to [pump] less and less water,” he says.
How and when the megadrought affecting huge swathes of North America will ultimately end is extraordinarily difficult to predict. Previous megadroughts that have occurred around the world over past millennia provide some clues, but human-caused climate change is now making extreme drought more common and more severe.
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Every single county in California is now under a drought emergency proclamation. were unable to harvest crops because they didn’t mature due to water-stress, American food prices. Reservoirs like Lake Mead are drying up. And the as drying soils contract – in some places permanently reducing the amount of water that can be stored in the future.
“The trend is toward a much more arid environment under global warming,” says , a climate scientist at the Lamont-Doherty Earth Observatory of Columbia University, particularly in the American Southwest. He explains that defining the start and end of a megadrought can be tricky, because a drought can be defined by different variables, including precipitation changes, soil moisture or other aspects of the hydrological cycle. But by any measure, the western US is deep into an abnormally dry period.
When researchers like Smerdon try to establish how megadroughts end, they often look back at past geological periods for clues. A recurring climate pattern in the tropical Pacific Ocean known as the El Niño-Southern Oscillation (ENSO) – which brings predictable shifts in ocean surface temperature and rainfall known as La Niña and El Niño – is thought to play a big role in the swings between . “Lots of successive La Niñas give really dry periods, lots of predominant El Niños give wet periods,” says Smerdon.
Megadroughts themselves are part of natural cycles in western North America. In the last 1000 years, the worst period This may have caused the civilisations, including the abandonment of the Mesa Verde settlements in what is now south-western Colorado. Similar historic patterns can be seen globally; around , a megadrought appears to have stretched from the Indus Valley in South Asia all the way to Spain. Smerdon’s research shows that sometimes, the climate pattern shifts are dramatic, swinging from extended drought straight to very waterlogged intervals. By the middle of the 14th century, for example, heavy rainfall returned to the American West.
“Pluvials are the wet periods, and yin to megadroughts’ yang,” Smerdon says. A study published in Science Advances in August that, based on past trends, California was also overdue for a “catastrophic flood event”, a severe event that could dump 75 centimetres of rain in San Francisco and 250 centimetres in the mountains.
Yet as climate change disrupts these natural cycles, past patterns may no longer accurately predict future conditions. Sea surface temperatures and ocean circulation are changing, although scientists currently debate whether that will enhance or moderate how dry the Southwest becomes. To some extent, it is insignificant: “What’s really driving the aridification trend is increased temperatures,” says Smerdon. Warmer temperatures will spur evaporation from soil and plants, while hotter air can hold onto more moisture. The impact is so dramatic that even climate models which suggest the region’s precipitation will increase by 5-10 per cent still predict a parched future.
Those hoping soggier weather may finally be around the corner are likely to be disappointed: In a paper published in Nature this year, Smerdon and his colleagues reconstructed soil moisture records since AD 800 and predicted there is a that the current megadrought will last for at least another eight years. “Even if it’s a really wet year next year, it won’t just end,” says Smerdon, noting that reservoir capacities will probably take several wetter years to recover.
At a certain point, “it doesn’t make sense to keep using the same threshold or definition of drought”, says , a climate scientist at the University of California, Santa Barbara. She and her colleagues recently a study finding that, in the future, average conditions could resemble what today we would consider extreme drought, with potential periods of severe rainfall. “In the future, what we’d consider really dry now will be normal. By today’s standards, we’ll be in a drought all the time.”
This drift toward multiple and simultaneous extremes will make hazards more difficult to plan for. “Even during extremely severe droughts, you can get very intense rainstorms,” says Stevenson, “but the impacts could be more severe, because the ground is dried out.” Stevenson’s colleague Danielle Touma recently used computer models to explore the likelihood that catastrophic wildfires would be closely followed by heavy rain, a combination that can cause dangerous flash floods and mudslides; the risk would increase by eight times in the Pacific Northwest and double in California by the end of the century.
These moving baselines require a serious reckoning. “Our idea of what we should expect should continuously change,” says Stevenson. California may not see a true end to the current megadrought, even if it begins to rain again. “It might not mean going back to the same amount of moisture available when this megadrought started, because what is normal has shifted” during the last two decades, she says. Her recently published research used a definition of drought based on soil moisture conditions between the 1960s and 1990s. “We’re already outside of those bounds. We’re not going to go back to what was normal in the 80s, ever – until we start doing something about climate change.”
As a result, major questions now loom over the West’s economy and residents. “A lot of people are starting to realise that things are going to need to change sooner than we had anticipated,” says , associate director and research fellow at the Public Policy Institute of California’s Water Policy Center. In 2017, the institute on ways the San Joaquin Valley can adapt, engaging community members around the valley to find solutions to prevent, as Peterson puts it, “this land just becoming a dust bowl”. Some of the proposed tactics include switching to “”, or switching to crops that can be flexible in when and how much irrigation they need. She says storing more water in the ground through techniques that help recharge aquifers will also be key.
“The California population and agriculture has simply overgrown its water supply. Now the issue is, who gets what water’s left?”
None of the changes will be easy. Farmers have many fixed costs, and the decision to abandon fields that can’t be watered or to switch to less water-intensive crops with lower price points will eat into thin profit margins. New problems are also likely to arise: If flood irrigation becomes less common, salt can build up in soils, harming yields even for crops that need less water. In the Sacramento Valley, rice farms have replaced many wetlands, so if fields lie idle, migratory birds may lose critical feeding grounds.
Norman says that he knows many farmers in the San Joaquin Valley south-east of San Francisco who are now considering moving out of the state to places that still have water, like Idaho or the Midwest. “But if you wait too long to make that move, you can’t,” he says, as land loses value along with its diminishing water access. Given the difficulty of making a living in agriculture, he has taken a job off the family farm – as an engineer at a nearby water district, where he deals with permitting and design of water infrastructure. “We’re one of the few districts that use natural streams to deliver water to agriculture users,” he says, “so as we deliver, we’re also recharging water through creeks.” The job has given him an inside look at both sides of the problem. “The California population and agriculture has simply overgrown its water supply. Now the issue is, who gets what water’s left?”
Many are already feeling the impacts. Last year, drought removed almost from agriculture in California, cutting at least 14,000 jobs and resulting in $1.7 billion in losses. But Peterson says the right interventions might provide multiple benefits. Government support could help farmers shift where and what they plant, keeping roots in the ground and improving air quality. “There will be a lot of hard choices to make,” says Peterson. “But the rubber is going to start hitting the road here pretty soon.”
For his part, Smerdon says the long-term solution has to be taking action on climate change. “There’s a lot of anxiety about what we’re witnessing, but at the end of the day, the last thing you want to do is curl into a fetal position,” he says. “The solution is not to do nothing, but in fact to work harder – and more earnestly – to make sure the worst doesn’t come to pass.”
