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Earth’s terrestrial water storage has significantly declined in recent years, revealing a troubling trend that extends beyond just the melting of ice caps. Research published in the journal Science on March 28 indicates that the volume of water held in various terrestrial sources—including underground aquifers, lakes, rivers, and even soil moisture—has diminished by trillions of metric tons during the early 21st century.
This reduction is primarily influenced by global temperature increases, affecting both inland areas and oceanic environments. As temperatures rise, the frequency of drought conditions has escalated, which, coupled with anticipated continued warming, suggests that the trend of decreasing freshwater resources will persist, according to geophysicist Ki-Weon Seo from Seoul National University and his research team.
The analysis involved multiple independent methodologies, spanning timescales from 2000 to 2020. These approaches included satellite gravity measurements, soil moisture assessments using remote sensing, and observations of global sea level changes, in addition to tracking distortions in Earth’s rotation attributed to mass redistribution. Notably, the shift in water from land to oceans has resulted in a minor drift of Earth’s poles, measuring approximately 45 centimeters.
Collectively, the evidence highlights a marked and ongoing deterioration in terrestrial water reserves. From 2005 to 2015—an overlapping timeframe for various assessments—researchers noted a reduction of roughly 1.3 trillion metric tons in water storage. This decrease corresponds to a global sea level rise of approximately 3.5 millimeters, emphasizing the broad implications of freshwater loss on climate dynamics.
Significantly, the loss of soil moisture is particularly alarming due to its critical relationship with drought conditions. Data reveal that from 2000 to 2002, soil moisture decreased dramatically, losing an estimated 1.6 trillion tons. This substantial loss contributed to nearly two millimeters of sea level rise each year during that period. Comparatively, melting ice from Greenland contributed about 900 billion tons per year, or approximately 0.8 millimeters annually—less than half the soil moisture’s influence on sea levels.
The decline in soil moisture continues at a slower pace, with an additional estimated loss of about 1 trillion tons from 2003 to 2016. Rising temperatures in both the atmosphere and oceans are the primary drivers of this phenomenon. Recent decades have seen alterations in precipitation patterns while enhancing evaporation and transpiration—the process by which moisture is released into the atmosphere through plants.
Although increased evaporation can lead to fleeting episodes of heavy rainfall, much of this precipitation fails to reach the soil, resulting instead in runoff that ultimately flows into the oceans. Environmental scientists, such as Katharine Jacobs from the University of Arizona, point out that as average global temperatures rise, areas experiencing drought are expanding significantly compared to those seeing increased moisture from rainfall.
Groundwater extraction is another critical factor contributing to the declining water reserves. Jacobs notes that many professionals involved in water management might overlook the correlation between groundwater depletion and sea level rise—despite these changes being both measurable and influential on the shifting axis of the Earth.
Research findings underscore that the total water available in Earth’s soils has been on a downward trajectory since the dawn of the new millennium. Given current projections regarding climatic conditions, it is unlikely that these water reserves will recover. “Everything needs water. If you don’t have enough, you’re in trouble,” concludes Benjamin Cook, a climate modeler at NASA’s Goddard Institute for Space Studies.
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