California's sudden jump from withering drought to violent floods is a warning for the whole world

• A chain of atmospheric rivers is raining on drought-stricken California, causing deadly floods.
• Drought can make flood hazards worse by leaving brittle trees and landslide-prone wildfire scars.
• This drought-flood weather whiplash is becoming more common and severe as global temperatures rise.

A powerful cyclone walloping California is the latest in a series of atmospheric rivers flooding the state, briefly puncturing a years-long drought.

These rivers — long, narrow streams of water vapor traveling from the tropics — can carry as much water as the average flow at the mouth of the Mississippi River.

On Wednesday night, a new one pummeled Northern California with powerful winds and rain, leading to evacuation orders, road closures, and power outages for nearly 170,000 homes.

A toddler died after a tree crashed into a house, local paper The Press Democrat reported, and a 19-year-old died after losing control of her vehicle on a flooded road, according to police.

Much of the rain fell on ground that was already saturated from a similar storm that flooded the area on New Year's Eve. Those floods caused landslides and sinkholes, stranded people in flooded cars and newly formed islands, and breached levees.

In some places, waters from the New Year's storm hadn't even receded before the next deluge arrived.

Yet another atmospheric river is forecast to ride on this storm's tails over the weekend, and still another may follow next week. Each rainfall event could layer on more and more flooding.

California is getting both drier and wetter

"Everyone assumes that California's getting drier," Daniel Swain, a climate scientist at the University of California, Los Angeles, told Insider. "It almost universally comes across as a surprise that it's actually more likely that Northern California sees more rain in the future than less — even as it sees more severe droughts."

In a counterintuitive twist, both droughts and floods are becoming more severe in California. The state is getting both drier and wetter.

Like in many places across the globe, that double whammy makes it harder to adjust to the changing climate.

Swain calls this "hydroclimate whiplash" — the sudden jump from withering drought to violent floods. It happened last year in the Midwest, the Southwest, China, Pakistan, Australia, and Western Europe.

Swain and other scientists are finding that climate change drives more and more of this weather whiplash worldwide.

"You can really go to any continent, in any season, and find something at this point," Swain said.

Droughts and fires can make flooding more hazardous

Historic drought across California left parched soils ready to drink up the winter rains, but it also created new hazards for flooding.

Mass tree die-offs in both forests and cities have left behind brittle skeletons that are prone to collapse in heavy winds. Those falling trees and branches can damage property and knock out power during storms.

Drought has also made wildfires more ravenous, leaving behind larger burn scars, which bring their own flood hazards. Areas scarred from wildfire are prone to mudslides and flash floods during heavy rainfall.

Though climate change isn't necessarily causing California's drought, it's probably contributing to it, as rising temperatures dry out soil and vegetation. Scientists expect droughts to become more common and more intense as global temperatures continue to rise in the coming years, according to the latest report from the UN's Intergovernmental Panel on Climate Change.

At the same time, California's wet season is becoming wetter and more violent.

Atmospheric rivers can dump more rain as temperatures rise

A basic rule of thermodynamics is driving more severe rainfall events all over the world: Warmer air has a greater capacity to carry water vapor.

For every temperature increase of 1 degree Fahrenheit, the atmosphere gains 4% more water-carrying capacity. So as the planet warms, it exponentially raises the ceiling for how much water an atmospheric river can carry and dump on California.

"We can't even really get used to the rate of change. We need to get used to an increasing rate of change," Swain said, comparing the exponential rise to compound interest in a bank account.

Already, average summer temperatures in California have risen 3 degrees Fahrenheit, according to the Scripps Institution of Oceanography. Researchers there forecast that atmospheric rivers are strengthening and becoming the dominant source of precipitation in the state.

California's rainfall is likely to come in fewer, more dramatic bursts, disrupting extended dry periods.

That means the cost of flood damages from atmospheric rivers could triple by the end of the century if humans don't reel in greenhouse-gas emissions, according to another Scripps study.

"It's not too late to limit the risk," Tom Corringham, a climate economist who led the study, said in a press release in August. "Reductions in greenhouse gas emissions could significantly reduce projected damages."

Weather whiplash is here to stay, and it will probably get more severe

California's mid-drought deluge is just an example of a global trend: Normal weather patterns are getting more extreme, and weather whiplash is the new norm.

These violent swings between dry and wet events are projected to happen more frequently and grow more severe in the coming decades, especially if emissions continue to rise.

Three recent studies show that increasing drought-flood whiplash is more than a projected future. In California, it's already here, and scientists can see it happening in their data.

"As recently as a few years ago, it was sort of a prediction," Swain said. "Now we're starting to see it as a reality."