All of Earth’s continents have experienced “unprecedented freshwater loss” driven by climate change, unsustainable groundwater use and extreme droughts since 2002, new satellite observations have revealed. 

A study led by a team at Arizona State University found four continental-scale “mega-drying” regions located in the northern hemisphere that could have significant consequences for water security, agriculture and sea levels.

The researchers evaluated more than two decades of data from the Gravity Recovery and Climate Experiment (GRACE) and GRACE-Follow On (GRACE-FO) missions, a collaboration between Nasa and the German Aerospace Center. The studies looked at how terrestrial water storage – which includes all of Earth’s surface and vegetation water, soil moisture, ice, snow and groundwater stored on land – had changed since 2002.

Drying areas on land were found to be expanding at a rate roughly twice the size of California every year, and the rate at which dry areas are getting drier outpaced the rate at which wet areas were getting wetter.

The study found that 75% of the world’s population lived 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 melting 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. 

“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 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 also revealed that, after 2014, the drying regions seemed to have 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. And in Canada and Russia, snow, ice and permafrost melting increased over the last decade, with the continued depletion of groundwater globally is a major factor.

“This study really shows how important it is to have continuous observations of a variable such as terrestrial water storage,” said Hrishikesh Chandanpurkar, lead author of the study. “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.”