Subsidence, or gradual sinking of the land, could affect 19% of the world’s population by 2040, according to a new survey funded by UNESCO.
If no action is taken, human activity, combined with drought and rising sea levels exacerbated by global warming, could put many of the world’s coastal cities at risk of serious flooding.
Jakarta has sunk more than 2.5 meters in the past 10 years, causing the Indonesian government to relocate the country’s capital to the island of Borneo.
In Europe, subsidence is responsible for placing 25% of the Netherlands below sea level. Flat coastal regions, as well as urban and agricultural centers in dry climates, are at greater risk.
Gerardo Herrera-García, chief researcher of the project, linked to the Spanish Geological and Mining Institute, said: “Densely populated areas or areas that need irrigation for agriculture because they are located in dry places for long periods of time, they need to pump underground water. When they pump water, the aquifer’s natural recharge is less than the volume of water they are pumping ”.
This extraction of water from the soil causes the surface to sink. But the lack of pumping regulations and the rapid increase in the human population are the most likely factors that contribute to subsidence rates.
In Iran, the population has more than doubled in the past 50 years, while groundwater pumping has remained unregulated. The country’s cities are now among the urban centers that sink the most in the world, falling by up to 25 centimeters each year.
Although subsidence was a common problem throughout the 20th century, it was previously analyzed only in a local context.
The new project, developed by an international team of scientists, sought to consolidate existing research. The scientists produced a universally applicable model to predict which areas were most at risk of subsidence.
The results showed that subsidence was a global problem, linked to global warming and also unsustainable agricultural practices. “The world’s largest aquifers are being depleted for agricultural purposes,” said Herrera-García.
According to Herrera-García, groundwater in the United States, Mexico, China and India is being drained quickly to meet global food demand. Continued subsidence in these areas will affect populations worldwide. Making global food production sustainable was possible, said Herrera-García, but the problem would have to be resolved soon.
In addition, global warming is expected to cause prolonged periods of drought, which will accelerate the rate of subsidence as more water is pumped out of the ground.
Meanwhile, sea levels are expected to rise to one meter in the next century. This means that more coastal cities will face the same problems as Jakarta, as more areas will be subject to flooding.
However, Herrera-García said that while subsidence is a major threat to the global environment, it could be fixed much more easily than climate change. Technologies, such as satellites and radars, can quickly identify areas of subsidence, while “simple policies and tools” can be used by local authorities to tackle the problem effectively.
“In Tokyo, they had a major subsidence problem in the first part of the last century. They implemented groundwater regulations and solved the problem. “
Other solutions for subsidence include finding alternative sources of water, practicing efficient agriculture to use as little water as possible and injecting water back into aquifers.
“These solutions are the same everywhere and can be applied to both large aquifers and smaller aquifers,” said Herrera-García. “I think we are on time. The solutions are there and it’s time to implement them. “