21 March 2024

Land subsidence threatens 2 billion people

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Subsidence, or the lowering of the land surface due to the removal of material from underground, impacts 25 percent of the Planet’s population, U.S. researchers have found

by Matteo Cavallito

 

Subsidence, or the lowering of the land surface due to the removal of material from underground, is an increasingly common phenomenon on a global scale. To the point of potentially impacting 25 percent of the Planet’s population. That is roughly two billion people. This is supported by a study published in the journal Geophysical Research Letters.

Behind the phenomenon there could be several factors, a statement by the researchers points out. The list includes natural causes, such as earthquakes, volcanic activity and compaction of unconsolidated fine-grained sediments. But also human interventions such as, for example, mining and groundwater extraction. Progressive ground sinking, in particular, is “a major issue in urban zones where it can cause building collapse.”

The study

The investigation, which involved a team of scientists led by Tsimur Davydzenka, a researcher at the Colorado School of Mines, relied on artificial intelligence to advance a planet-wide estimate. “Land subsidence is a destructive phenomenon occurring around the globe causing damage to infrastructure, increased flood risks, and reduction of aquifer storage,” the study explains.

“However, prediction and quantification of land subsidence rates globally using physics-based methods presents a major challenge.”

By taking advantage of modern deep learning methods – a field of research focused on particular learning patterns in artificial intelligence – and making use of the increasing availability of data on environmental parameters, the study thus allowed the researchers to describe the phenomenon on a global scale. “The resulting map can be used for various geospatial modeling tasks, as well as to guide a more detailed local investigation of land subsidence.”

One in four humans is at risk

The researchers used existing data from additional studies and remote sensing to enable analysis of a total of 46,000 scenarios. These were supplemented by a selection of 23 different climatic, geographic and topographic conditions (including precipitation, soil composition, sediment thickness and slope). All this information was used to train a machine learning model that was then able to estimate the total area at risk.

In total, the study states, “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.”

“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.”

L’estrazione di acqua sotterranea è il principale fattore di subsidenza a livello globale. Immagine: Davydzenka et al. “Unveiling the Global Extent of Land Subsidence: The Sinking Crisis”, Research Letter 20 febbraio 2024 https://doi.org/10.1029/2023GL104497 CC BY 4.0 DEED

Groundwater extraction is the main driver of subsidence globally. Image: Davydzenka et al. “Unveiling the Global Extent of Land Subsidence: The Sinking Crisis”, Research Letter 20 febbraio 2024  CC BY 4.0 DEED

Asia is the most affected region

During the study, researchers identified 2.1 million square kilometers of cropland threatened by the phenomenon. Subtropical highlands and temperate oceanic climates experienced subsidence rates greater than 50 millimeters per year, “while the tropical rainforest climate is characterized by the largest subsidence extent,” the study says.

South Asia is characterized by the largest extent of the phenomenon globally, with 2.2 percent of its total area affected by subsidence greater than 50 millimeters per year impacting 20 million people.

Globally, the top five countries by average subsidence are the Philippines, Iran, Costa Rica, Indonesia and Uzbekistan. The top five by extent of the phenomenon are China (with more than 1,000 km2), Indonesia, Iran, India and Pakistan. Leading the list by number of people affected by the phenomenon is India, with 633 million individuals. The single highest rate of subsidence was recorded in Mexico: 320.5 mm/year.

Groundwater extraction is the main factor in subsidence

The analytical model used by artificial intelligence determined that groundwater extraction is the most important factor in predicting the phenomenon by preceding seismic activity and precipitation, among others. To reduce dependence on deeply placed water, the researchers say, it is therefore appropriate “promoting water use efficiency, implementing strict regulatory frameworks and incentivizing agricultural practices that optimize water consumption.”

In addition, it is important investing in recycling technologies starting with harnessing alternative sources such as treated wastewater and rainwater harvesting. By integrating conservation practices, using technological innovations and diversifying water sources, the scientists say, it is therefore possible to build a sustainable water supply system thereby mitigating environmental impacts.