Satellite imaging shows the emergence of four continental-scale “mega-drying” regions, each located in the northern hemisphere.
For over two decades, satellites have documented a major crisis unfolding beneath our feet: Earth’s continents are drying out at unprecedented rates. Fueled by climate change, groundwater overuse, and extreme drought, this trend has carved out four massive “mega-drying” regions across the northern hemisphere, threatening freshwater supplies for billions.
The findings show how groundwater loss alone contributes more to sea level rise than melting ice sheets, and unless urgent global water policies are enacted, we could face a catastrophic freshwater bankruptcy.
Continental drying
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.
Researchers from Arizona State University report that drying areas on land are expanding at a rate roughly twice the size of California every year. Furthermore, 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.
This threatens agriculture and food security, biodiversity, freshwater supplies and global stability.
2014 to 2015 was the tipping point
The scientists 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.
The findings are based on over 22 years of terrestrial water storage data from US-German GRACE and GRACE-FO satellite missions.
The implications of this for available freshwater are significant, in that 75% of the world’s population live 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 and 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.
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.
According to lead researcher Jay Famiglietti: “These findings send perhaps the most alarming message yet about the impact of climate change on our water resources…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.”
Going forwards
This study really shows how important it is to have continuous observations of a variable such as terrestrial water storage.
The research appears in the journal Science Advances, titled “Unprecedented continental drying, shrinking freshwater availability, and increasing land contributions to sea level rise.”
