Two decades of satellite observations reveal a grim global warning: Huge swathes of Earth's continents are drying out at an unprecedented rate. Driven by climate change, groundwater overexploitation and increasing droughts, this "superdrought" phenomenon is already contributing more to rising sea levels than melting ice caps. Four vast arid zones - stretching from North America to Eurasia and North Africa - are forming, threatening water supplies for billions of people.

New findings from more than two decades of satellite observation research show that since 2002, Earth's continents have experienced unprecedented freshwater losses due to the impact of climate change, unsustainable groundwater use and extreme drought. The study, led by Arizona State University and published today in Science Advances, highlights the emergence of four continent-scale "hyperarid" regions, all in the Northern Hemisphere, and warns that they will have serious consequences for water security, agriculture, sea level rise and global stability.

Dry areas on land are expanding annually at a rate roughly twice the size of California, the team reports. Moreover, dry areas are now drying out faster than humid areas are wetting, upending long-standing hydrological patterns.

The negative impact this has on available freshwater resources is alarming. 75% of the world's population lives in 101 countries that have been reducing their freshwater resources over the past 22 years. According to United Nations projections, the world's population is expected to continue to grow over the next 50 to 60 years, while at the same time freshwater resources are shrinking dramatically.

Since 2002, Earth's continents have experienced unprecedented freshwater losses due to climate change, unsustainable groundwater use and extreme drought. A new study led by Arizona State University highlights the emergence of four continent-scale "hyperarid" regions, all in the Northern Hemisphere, with alarming impacts on freshwater supplies. Photo credit: Sophia Franz

Groundwater: the hidden culprit

Researchers identified the types of water loss on land and found for the first time that 68% of water loss comes from groundwater alone - contributing more to sea level rise than glaciers and ice sheets on land.

"These findings are perhaps the most alarming information yet about the impact of climate change on our water resources," said the study's lead researcher Jay Famiglietti, a professor of global futures in the School of Sustainability at Arizona State University. "Continents are drying up, freshwater supplies are dwindling and sea level rise is accelerating. The consequences of continued overuse of groundwater could jeopardize the food and water security of billions of people around the world. This is an 'all hands on deck' moment - we need to act now to safeguard global water security."

This figure shows the long-term trend of terrestrial water reserves in each country observed by the GRACE/FO satellite (February 2003 to April 2024). Image credit: Arizona State University and the Virtue GRACE and GRACE-FO missions.

Tracking water trends from space

Researchers evaluated more than two decades of data from the Virtue Gravity Recovery and Climate Experiment (GRACE) and GRACE-Follow On (GRACE-FO) missions to examine how and why terrestrial water reserves have changed since 2002. Terrestrial water reserves include all water on the Earth's surface and vegetation, soil moisture, ice, snow, and groundwater stored on land.

"It's staggering that we are losing so much non-renewable water," said the study's lead author, Hrishikesh A. Chandanpurkar, a research scientist at Arizona State University. "Glaciers and deep groundwater are like ancient trust funds. Instead of tapping them only when we need them, such as during long droughts, we take them for granted. Additionally, we don't try to replenish groundwater systems during wet years, so freshwater resources are being depleted."

Jay Famiglietti is a professor of global futures at Arizona State University. Image source: Arizona State University

Global drought tipping point

The study found that there appears to be a turning point around 2014-2015, during the so-called "Super El Niño" period. Extreme climate events began to accelerate, bringing with them increased groundwater consumption and continental droughts outpacing the melting of glaciers and ice caps.

In addition, the study revealed a previously unreported fluctuation in that after 2014, dry areas shifted from being mainly located in the Southern Hemisphere to being mainly located in the Northern Hemisphere, while the reverse was true for humid areas.

One of the key factors driving continental aridification is the increase in extreme drought events in mid-latitude regions of the Northern Hemisphere, such as Europe. In addition, the melting of ice, snow and permafrost has intensified in Canada and Russia over the past decade, and the continued depletion of groundwater around the world is also a major factor.

In previous research, team members studied terrestrial water reserves using satellite data from 2002 to 2016. In the new study, the team analyzed more than 20 years of data and discovered a key major development in the continent's aridification. Several regional drought patterns, as well as previously identified local "hotspots" of terrestrial water storage loss, are now interconnected to form four continent-scale mega-arid zones.

These areas include:

Southwestern and Central America: This region includes the major grain-producing regions of the southwestern United States, as well as major desert cities such as Phoenix, Tucson, and 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, melting snow and permafrost in high latitudes in Canada, and drought in major agricultural regions such as British Columbia and Saskatchewan

Northern Russia: The region is experiencing heavy snowfall and melting permafrost in high latitudes

Middle East-North Africa (MENA) Pan-Eurasia: This region includes major desert cities such as Dubai, Casablanca, Cairo, Baghdad, and Tehran; major food-producing regions such as Ukraine, northwestern India, and the North China Plain region; the shrinking Caspian and Aral Seas; and major cities such as Barcelona, ​​Paris, Berlin, Dhaka, and Beijing.

Surprising latitudinal trends

In fact, research shows that only average latitudes in the tropics have continued to become humid since 2002, and this was not predicted by the IPCC's (Intergovernmental Panel on Climate Change) climate models (sophisticated computer programs used to predict future climate scenarios). Continuous records are critical to understanding long-term changes in the water cycle.

"This study really shows the importance of continuous observations of variables such as terrestrial water storage," Chandanpurkar said. "The GRACE record has reached a point where we can clearly see long-term trends in climate change. More in-situ observations and data sharing will further support this separation and inform water resource management."

Hrishikesh A. Chandanpurkar, Research Scientist, Arizona State University. Image credit: Hrishikesh A. Chandanpurka

Unprecedented continental drought threatens agriculture and food security, biodiversity, freshwater supplies, and global stability. This study highlights the need for continued large-scale research to inform policymakers and communities about growing water challenges and seize opportunities to create meaningful change.

"This study is significant. It clearly demonstrates the urgent need for new policies and groundwater management strategies globally," Famiglietti said. She currently works at the Julie Ann Wrigley Global Futures Laboratory and was a senior water scientist at NASA's Jet Propulsion Laboratory. "While efforts to mitigate climate change face challenges, we can address continental drought by implementing new policies around regional and international groundwater sustainability. This, in turn, will slow the rate of sea level rise and help protect water resources for future generations."

Suggestions for action

The study calls for immediate action to slow and reverse groundwater depletion, protect remaining freshwater resources, and address growing water scarcity and coastal flooding risks. The research team further stated that strategic water management, international cooperation and sustainable policies are critical to protect water resources for future generations and mitigate further damage to the earth system.

The research will also support an upcoming flagship report from the World Bank Group, which will delve into these findings, including the human and economic impacts of the continent's drying out, and propose actionable solutions for countries to address the growing freshwater crisis.

The findings are based on more than 22 years of terrestrial water storage data from the joint US-German GRACE and GRACE-FO satellite missions. The full report details scientific analysis and regional breakdown of drought trends. Drought trends remain strong and persistent despite climate change.

Compiled from /scitechdaily