Finer satellite maps raise aquifer depletion estimates 45 percent in irrigated regions

Both figures are comparisons against earlier published estimates, not raw drawdown rates. The team reworked 23 years of satellite measurements at finer spatial scale and found the same regions moving more water than coarser analyses had shown ^[25][2].

Across all regions with above-background trends, the sharpening added 33 percent on average ^[3]. In the aquifer-pumping regions it added 45 percent, about 1.36 times as large a revision and 12 percentage points above the global average ^[1][22].

Resolution matters for a second reason. "Earlier studies could see broad patterns of long-term freshwater loss or gain but couldn't reliably tell how much was due to human activity versus climate swings, in part due to resolution limitations," Mary Michael Forrester O'Neill, the first author and a researcher at the University of Maryland's Earth System Science Interdisciplinary Center and the Hydrological Sciences Laboratory at NASA's Goddard Space Flight Center, told Live Science in an email ^[7][6]. "This study sharpened the picture and used geostatistical methods to rank the impacts of human causes, like irrigation and dam building, against climate factors, like rainfall and drought," she said ^[8].

That ranking produced the hotspot list. Twenty-two regions gained water, from rain-fed farming, surface-water irrigation, reservoir impoundment and deforestation ^[11][15]. One of them is the part of central Russia holding the Boguchany Reservoir, filled in 2012 after a hydroelectric dam was built. Eighteen lost water, to groundwater irrigation and to canals, diversions and other infrastructure ^[12]. The losses outweighed the gains overall ^[4].

The authors note that local gains and losses alike may cut freshwater availability downstream or in the surrounding region ^[24].

Terrestrial water storage is a regional total, so a trend in it will not tell a grower the depth to water in a particular bore, and the driver ranking is a statistical attribution ^[3][8]. Live Science's account names water managers and downstream communities as the intended users. It does not report a validation against well records, or any test of the commercial water-risk models used in farming and finance ^[23]. "Water managers and downstream communities need to know which aquifer, reservoir, or irrigation district is responsible for a given trend in large-scale freshwater storage, not just that 'somewhere in this country, water is being lost,'" Forrester O'Neill said ^[10].

Earlier work had already flagged the US High Plains, California's Central Valley, northern India, Pakistan, North China and the Fertile Crescent as places that consistently overuse groundwater ^[17]. "Within these regions, we found the pace of depletion is considerably more severe than earlier estimates suggested, reinforcing food security concerns," O'Neill said ^[18].

Hrishikesh Chandanpurkar, a hydrologist and co-founder of the nonprofit Evergreen Resilience Institute who was not involved in the study, said the very high resolution is one of the paper's novelties; he led a study last year describing mega-drying regions and co-authored a report on continental drying ^[19]. "It has become very dire in a lot of places," he told Live Science ^[5].

The paper, published Sept. 14 in PNAS, reports human water use as a significant driver of storage change on every continent except Australia and Antarctica, where O'Neill said climate factors are more influential ^[13][14].