Nearly 2 billion people globally at risk from land subsidence
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With an increase in land subsidence occurring in densely populated areas, a key factor driving subsidence is groundwater abstraction—the removal of water stored in the pore space of subsurface layers and transporting it away for human consumption and irrigation in agriculture, leading to compaction of the subsurface sediments.
This is the focus of new research, published in Geophysical Research Letters, in which scientists identified a significant positive correlation between the rate of groundwater abstraction and subsidence, meaning these areas should be a major focus of water resources management to alleviate this geohazard.
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They determined that more than 6.3 million km2 of Earth's surface (~5% of total global land area) is susceptible to subsidence rates deemed significant enough to cause damage and require mitigation strategies—these being greater than 5 mm/y. This follows from previous work that had suggested 12 million km2 of land surface experienced subsidence rates of 430 mm/y. Of this more than 6.3 million km2, 231,000 km2 was identified in urban areas, where population density shows ~2 billion people (25% of global population) are located in these high-risk zones.
The machine learning model determined groundwater abstraction to be the main predictor of land subsidence, followed by seismic activity from earthquakes, then environmental conditions (namely precipitation) affecting groundwater recharge, sedimentary unit thickness (larger units having more space for ultimate compaction), mean temperature of warmest months (important for arid and semi-arid regions susceptible to subsidence), soil clay content, and population density.
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