New global study shows freshwater is disappearing at alarming rates
Unprecedented continental drying driven by severe droughts and groundwater overuse are reducing freshwater and contributing to sea level rise
Arizona State University
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Earth’s continents have experienced unprecedented freshwater loss since 2002, driven by climate change, unsustainable groundwater use and extreme droughts. A new Arizona State University-led study highlights the emergence of four continental-scale “mega-drying” regions, all located in the northern hemisphere, with staggering implications for freshwater availability.
view moreCredit: Image by Sophia Franz
New findings from studying over two decades of satellite observations reveal that the Earth’s continents have experienced unprecedented freshwater loss since 2002, driven by climate change, unsustainable groundwater use and extreme droughts. The study, led by Arizona State University and published today in Science Advances, highlights the emergence of four continental-scale “mega-drying” regions, all located in the northern hemisphere, and warns of severe consequences for water security, agriculture, sea level rise and global stability.
The research team reports that drying areas on land are expanding at a rate roughly twice the size of California every year. And, the rate at which dry areas are getting drier now outpaces the rate at which wet areas are getting wetter, reversing long-standing hydrological patterns.
The negative implications of this for available freshwater are staggering. 75% of the world’s population lives in 101 countries that have been losing freshwater for the past 22 years. According to the United Nations, the world’s population is expected to continue to grow for the next 50 to 60 years — at the same time the availability of freshwater is dramatically shrinking.
The researchers identified the type of water loss on land, and for the first time, found that 68% came from groundwater alone — contributing more to sea level rise than the Greenland and Antarctic ice sheets combined.
“These findings send perhaps the most alarming message yet about the impact of climate change on our water resources,” said Jay Famiglietti, the study’s principal investigator and a Global Futures Professor with the ASU School of Sustainability. “Continents are drying, freshwater availability is shrinking, and sea level rise is accelerating. The consequences of continued groundwater overuse could undermine 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.”
The researchers evaluated more than two decades of data from the US-German Gravity Recovery and Climate Experiment (GRACE) and GRACE-Follow On (GRACE-FO) missions, looking at how and why terrestrial water storage has changed since 2002. Terrestrial water storage includes all of Earth’s surface and vegetation water, soil moisture, ice, snow, and groundwater stored on land.
“It is striking how much non-renewable water we are losing,” said Hrishikesh A. Chandanpurkar, lead author of the study and a research scientist for ASU. “Glaciers and deep groundwater are sort of ancient trust funds. Instead of using them only in times of need such as a prolonged drought, we are taking them for granted. Also, we are not trying to replenish the groundwater systems during wet years and thus edging towards an imminent freshwater bankruptcy.”
Tipping point and worsening continental drying
The study identified what seems to be a tipping point around 2014-15 during a time considered “mega El-Niño” years. Climate extremes began accelerating and in response, groundwater use increased and continental drying exceeded the rates of glacier and ice sheet melting.
Additionally, the study revealed a previously unreported oscillation where after 2014, drying regions flipped from being located mostly in the southern hemisphere to mostly in the north, and vice versa for wet regions.
One of the key drivers contributing to continental drying is the increasing extremes of drought in the mid-latitudes of the northern hemisphere, for example, in Europe. Additionally, in Canada and Russia, snow, ice, and permafrost melting increased over the last decade, and the continued depletion of groundwater globally is a major factor.
In a previous study, members of the team studied terrestrial water storage from satellite data spanning 2002 - 2016. In the new study, the team looked at more than 20 years of data and discovered a critical, major development in continental drying. Several regional drying patterns and previously identified localized ‘hotspots’ for terrestrial water storage loss are now interconnected — forming the four continental-scale mega drying regions.
These include:
Southwestern North America and Central America: this region includes major food-producing regions across the American Southwest, along with major desert cities such as Phoenix, Tucson, Las Vegas, and major metropolitan areas such as Los Angeles and Mexico City.
Alaska and Northern Canada: this region includes melting alpine glaciers in Alaska and British Columbia, snow and permafrost melting across the Canadian high latitudes, and drying in major agricultural regions such as British Columbia and Saskatchewan
Northern Russia: this region is experiencing major snow and permafrost melting across the high latitudes
Middle East-North Africa (MENA) Pan-Eurasia: this region includes major desert cities including Dubai, Casablanca, Cairo, Baghdad and Tehran; major food producing regions including Ukraine, northwest India, and China’s North China Plain region; the shrinking Caspian and Aral Seas; and major cities such as Barcelona, Paris, Berlin, Dhaka and Beijing.
In fact, the study showed that since 2002, only the tropics have continued to get wetter on average by latitude, something not predicted by IPCC (Intergovernmental Panel on Climate Change) climate models — sophisticated computer programs used to project future climate scenarios. Continuous records are critical in understanding the long-term changes in the water cycle.
“This study really shows how important it is to have continuous observations of a variable such as terrestrial water storage,” said Chandanpurkar. “GRACE records are really getting to the length where we are able to robustly see long-term trends from climate variability. More in-situ observations and data sharing would further support in making this separation and inform water management.”
A Planetary Wake-Up Call
The unprecedented scale of continental drying threatens agriculture and food security, biodiversity, freshwater supplies and global stability. The current study highlights the need for ongoing research at scale to inform policymakers and communities about worsening water challenges and opportunities to create meaningful change.
“This research matters. It clearly shows that we urgently need new policies and groundwater management strategies on a global scale,” said Famiglietti, who is also with the Julie Ann Wrigley Global Futures Laboratory and a former Senior Water Scientist at NASA’s Jet Propulsion Laboratory. “While efforts to mitigate climate change are facing challenges, we can address continental drying by implementing new policies around regional and international groundwater sustainability. In turn, this will slow the rate of sea level rise and help preserve water for future generations.”
The study calls for immediate action to slow and reverse groundwater depletion, protect remaining freshwater resources, and adapt to the growing risk of water scarcity and coastal flooding. The research team goes on to say that strategic water management, international cooperation, and sustainable policies are essential to preserving water for future generations and mitigating further damage to planetary systems.
The research will also support an upcoming World Bank Group flagship report that will delve deeper into these findings, including the human and economic implications of continental drying, and present actionable solutions for countries to address the growing freshwater crisis.
About the Study
The findings are based on over 22 years of terrestrial water storage data from US-German GRACE and GRACE-FO satellite missions. The full report details the scientific analyses and regional breakdowns of the drying trends, which have proven robust and persistent despite climate variability.
The research team includes scientists from Arizona State University; Hrishikesh A. Chandanpurkar, FLAME University; John T. Reager and David N. Wiese, JPL; Kaushik Gopalan and Yoshihide Wada, King Abdullah University of Science and Technology; Kauru Kakinuma, Korea Advanced Institute of Science and Technology; and Fan Zhang, The World Bank.
This research was funded by the Julie Ann Wrigley Global Futures Laboratory at Arizona State University, the GRACE Follow-On Science Team, and World Bank Global Water Monitoring.
This figure shows the long-term terrestrial water storage trends from GRACE/FO averaged for every country (2/2003-4/2024).
Credit
Arizona State University and US-German GRACE and GRACE-FO missions.
Journal
Science Advances
Method of Research
Data/statistical analysis
Subject of Research
Not applicable
Article Title
Unprecedented Continental Drying, Shrinking Freshwater Availability, and 3 Increasing Land Contributions to Sea Level Rise
Article Publication Date
25-Jul-2025
Identifying landslide threats using hydrological predictors
Rainfall intensity, soil saturation and snowmelt drive widespread landslide pathways
Northwestern University
Northwestern University and University of California, Los Angeles (UCLA) scientists have developed a new process-based framework that provides a more accurate and dynamic approach to landslide prediction over large areas.
While traditional landslide prediction methods often rely solely on rainfall intensity, the new approach integrates various water-related processes with a machine-learning model. By accounting for diverse and sometimes compounding factors, the framework offers a more robust understanding of what drives these destructive events.
With further development, the new framework could help improve early warning systems, inform hazard planning and enhance strategies for climate resilience in regions vulnerable to landslides. Ultimately, these approaches could help save lives and prevent damage.
The study will be published on July 25 in Geophysical Research Letters.
“Current early warning systems tend to derive information from historical precipitation events and landslides,” said Chuxuan Li, the study’s first author. “Because it’s based on historical data, it doesn’t consider the changing climate. In the future, we expect more intense precipitation and higher numbers of heavy precipitation events. These systems often don’t consider snow melt or other ground conditions. Our model considers a wider range of factors, so we can identify more diverse pathways leading to landslides over a large spatial scale.”
“Different landslides can be caused by different hydrological processes,” said Northwestern’s Daniel E. Horton, the study’s senior author. “We’re trying to identify which landslides are caused by which processes. But we’re also trying to think about it from a much broader scale; a scale that is consistent with the storms that cause these events. Our ideal is to develop tools that could be useful across a broad region, such as the state of California.”
Horton is an associate professor of Earth, environmental and planetary sciences at Northwestern’s Weinberg College of Arts and Sciences, where he leads the Climate Change Research Group. Li is a Ph.D. graduate from Horton’s laboratory at Northwestern and current postdoctoral researcher at UCLA.
Simulating a ‘parade’ of storms
Dangerous flows of water, mud and rocks, landslides can be difficult to predict — especially across large areas with varied landscapes and different climates. To better understand how and why widespread landslides occur, the Northwestern and UCLA team looked to one month of extreme weather in California.
During the winter of 2022-23, California experienced an unprecedented “parade” of nine consecutive atmospheric rivers, which caused catastrophic flooding and more than 600 landslides. To understand the pathways that caused these landslides, the scientists adopted a community-developed computer model that simulates how water moves through the environment, including rain infiltrating into the ground, running off on the surface, evaporating, and freezing or melting of snow and ice.
To drive the model, the team used a diverse array of meteorological, geographical and historical data. This included information about terrain, soil depth, past wildfires, precipitation, and meteorological and climatic conditions.
Using model outputs, the team developed a metric, called “water balance status” (WBS), to assess when there is too much water in a particular area. A positive WBS means there’s more water than the ground can handle through absorption, storage, evaporation or drainage. This also means there’s higher potential for landslides.
Identifying main pathways
Finally, the Northwestern and UCLA team applied a machine-learning technique to group together similar landslides based on their sites’ specific conditions. Through this technique, they identified three main pathways that led to the California landslides: intense rainfall, rain on already saturated soils and melting snow or ice.
The team predicts that heavy, rapid downpours caused about 32% of the landslides. Roughly 53% of the landslides occurred after moderate rain fell on soils already saturated from previous storms. And about 15% of the landslides were linked to snow or ice, with rain accelerating the snowmelt or ice thaw.
“We found most of the landslides were triggered under excessively wet conditions,” Li said. “By excessively wet, we mean the precipitation exceeds the soil’s capacity to hold or drain water. This can be especially dangerous on steep slopes.”
When the scientists compared these events to their model, they found a significant majority (89%) of California’s landslides occurred in areas where the WBS was positive. This finding validated that the metric can accurately identify conditions ripe for landslides.
“While this study looks backwards to understand a past event, our ultimate goal is for the method to look forward to make predictions,” Horton said. “We plan to take this modeling framework that we developed and use it in concert with weather forecasting models.”
Better models for an uncertain future
As the global climate continues to change, prediction systems are more important than ever. Because warmer air can hold more water vapor, storms can dump more water. And more water often indicates more dangerous flooding and landslides.
In a recent review published in the journal Science, Horton and his collaborators examined how natural hazards, such as atmospheric rivers, often trigger other disasters to create a chain reaction. In the piece, the authors emphasize the critical need for integrating diverse datasets and building advanced models to improve the ability to predict and prepare for natural disasters.
“Atmospheric rivers are not necessarily becoming more common,” Horton said. “But, when they do make landfall, their impact is becoming more severe. Lately, we have seen an increase in the intensity of their precipitation. This is consistent with the global trend of experiencing more intense precipitation events due to human-caused climate change.”
The study, “Mixed hydrometeorological processes explain regional landslide potential,” was supported by the National Science Foundation (PREEVENTS grant numbers 1854951 and 2023112).
Journal
Geophysical Research Letters
Method of Research
Computational simulation/modeling
Article Title
Mixed hydrometeorological processes explain regional landslide potential
Article Publication Date
25-Jul-2025
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