The planet has endured massive freshwater losses over the past two decades due to the combined effects of climate change, overconsumption and drought, a new study has found.

Arid land areas are expanding at a rate roughly twice the size of California each year, according to the study, published in Science Advances. Dry spots are now drying up faster than wet areas are getting wetter — reversing historic hydrological patterns, per the research.

This continental-scale phenomenon of “mega-drying,” the study authors warned, could have severe consequences on water security, agriculture, sea level rise and global stability. Describing their results as “staggering,” the researchers determined that 75 percent of the world’s population lives in 101 countries that have been losing freshwater for the past 22 years

“These findings send perhaps the most alarming message yet about the impact of climate change on our water resources,” principal investigator Jay Famiglietti, a professor at Arizona State University’s School of Sustainability, said in a statement.

“Continents are drying, freshwater availability is shrinking, and sea level rise is accelerating,” Famiglietti added.

To evaluate changes in terrestrial water storage, the researchers combed through more than two decades of satellite observations — from April 2002 through April 2024 — from NASA’s Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On missions.

They defined terrestrial water storage as all of Earth’s surface and vegetation water, soil moisture, ice, snow and groundwater stored on land.

Ultimately, the researchers identified robust changes in these water storage levels since previous global studies.

These declines, they found, have been driven by high-latitude water losses in Russia and Canada, extreme in Central America and Europe and groundwater depletion — responsible for 68 percent of the losses alone.

The researchers also identified a “tipping point” in 2014-2015, years that meteorologists generally characterize as “mega El-Niño.” In North America, El-Niño years typically involve dryness and warmth in the northern U.S. and Canada, with increased flooding in the South.

Near the tipping point, climate extremes began accelerating, leading to a surge in groundwater use and continental drying-up that surpassed the rates of glacier and ice sheet melting, per the study.

Evaluating their 22 years of data, the scientists also determined that certain water storage loss “hotspots” previously assumed to be isolated were actually interconnected. These places, they concluded, make up four continental-scale, mega-drying regions.

The first region spans the U.S. Southwest, Mexico and Central America and includes many major food-producing regions. The second, meanwhile, includes Alaska and Northern Canada, which are stricken by snow and permafrost melt, as well as drying in agricultural zones.

Northern Russia, per the study, is the third region and is also undergoing considerable snow and permafrost melting in high latitude zones.

The fourth area, the Middle East-North Africa region and Pan-Eurasia, houses multiple major desert cities, food producing hubs, shrinking seas and urban cities, the researchers noted.

“It is striking how much non-renewable water we are losing,” lead author Hrishikesh Chandanpurkar, a research scientist at Arizona State, said in a statement.

“Glaciers and deep groundwater are sort of ancient trust funds,” he added. “Instead of using them only in times of need such as a prolonged drought, we are taking them for granted.”

Chandanpurkar also lamented the fact that humans are failing to replenish groundwater reservoirs during wet years and are thereby nearing “an imminent freshwater bankruptcy.”

Describing their findings as “a planetary wake-up call,” the authors stressed a need for ongoing research that can help inform policymakers about these dire water challenges.

The researchers also advocated for community-level opportunities to make meaningful change, particularly when it comes to excessive pumping of groundwater.

The consequences of overusing the remaining groundwater, Famiglietti warned, could threaten “food and water security for billions of people around the world.”

“This is an ‘all-hands-on-deck’ moment — we need immediate action on global water security,” he said.