Since 2002, each year the Earth’s drought-affected land area has grown by an average of about 848,000 square kilometres, a portion of land equivalent to the sum of Italy and France. Documenting this silent but steady expansion are data collected by the twin GRACE satellites—in orbit from 2002 to 2017—and their successor GRACE Follow-On, launched in 2018. The missions, jointly operated by NASA and the German Space Agency, have provided an unprecedented amount of information on changes in the Earth’s land mass, and in particular the distribution of fresh water, allowing scientists to map the evolution of drought conditions on a global scale.
A study recently published in the journal Science Advances by Arizona State University, in collaboration with other international research institutions, analysed this data over more than two decades. The picture that emerges is alarming: throughout the world, but with particular intensity in the Northern Hemisphere, large areas—termed “mega-regions”—are forming subject to chronic and progressive drought. The hardest-hit areas are concentrated along the west coast of North America, in Central America, the Middle East, South and Southeast Asia, and, more recently, Europe. The European continent, in particular, has experienced a sharp decline in water supplies over the past decade, in line with the drought waves that have affected countries such as Spain, France, Italy, Germany, and Hungary.
The main cause
The study highlights how climate change is the main structural cause of this transformation, but not the only one. Also weighing increasingly heavily is the unsustainable management of water resources, particularly groundwater aquifers. In many regions, the extraction of water from deep aquifers far exceeds their capacity for natural regeneration, leading to a progressive depletion of the subsoil. The research authors point out how this dynamic, if not corrected, risks leading to the depletion of entire nonrenewable aquifers in a relatively short time, with potentially irreversible consequences for agriculture, ecosystems and social stability.
An additional aggravating factor has been identified in the El Niño climate phenomenon, which since 2014 has contributed to further destabilisation of precipitation regimes in several areas of the planet, accelerating the reduction of surface and groundwater resources. This effect has added to a long-term trend already clearly discernible in GRACE data, which show how the progressive weakening of the hydrological cycle is leading to an uneven redistribution of freshwater, with increasingly wet areas on the one hand and vast regions becoming increasingly arid on the other.
A crucial tool
According to Matthew Rodell, a NASA hydrologist and one of the study’s co-authors, the GRACE satellites function as an orbital scale that can detect minute variations in the Earth’s land mass, thus providing a detailed snapshot of changes in water availability. These measurements, he explained, are now a crucial tool for understanding the combined impact of climate change and anthropogenic pressures on global water balances.
The implications of these findings are profound. Water scarcity is no longer a future threat, but a present reality in many areas of the world. The repercussions are already manifesting themselves today in the form of agricultural crises, forced migration, social tensions and geopolitical conflicts.
