A flooded agricultural field in Argentina. With kind approval
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A nearly unknown creature has awakened beneath the South American plains. The water table, the accumulation of groundwater underground, is increasingly rising in the region’s plains due to the loss of deep-rooted native vegetation and the imbalance between the water demands that the climate places on plants and the water demands that they can support. A phenomenon that is due to the rapid and violent expansion of agriculture, which leads to increasingly severe floods.
The depth at which the groundwater table lies varies depending on the harmony between water use and rainfall. This underground mantle is made up of solid particles, pieces of rock, organic remains, and empty spaces that retain fluid. In some regions of the southern hemisphere its levels are increasing. “Also known as Napa, it acts like a sponge under our feet: when all its pores are filled with water, it rises to the surface and creates permanent floods,” explains Esteban Jobbágy, agronomist and author of a study that shows the dramatic ecological impact shows the scenario that the Argentine pampas offers. Its plains have become a natural laboratory for assessing the hydrological impacts of dryland farming. One that has spread unchecked across the territory over the past 40 years.
As the study published in the journal Science shows, brutal deforestation and changes in land use are altering the water balance across much of South America. Forests of thorn trees, carob trees, savannahs and grasslands – drought-adapted vegetation of the Chaco-Pampeana ecoregion – which have been eliminated and replaced by annual dry crops in the last 40 years. “Fields cultivated for generations begin to fill with puddles that slowly turn into permanent lagoons, overflowing rivers and inundating entire cities in the provinces of Córdoba, San Luis and Santa Fé, among others,” says the scientist.
The change in the natural landscape in the last half of the century has its origins in the global demand for grain. A market that, according to the Food and Agriculture Organization of the United Nations (FAO), will skyrocket even further, leading to the rapid conversion of large swaths of native South American grasslands and forests into pure agricultural land. These flat landscapes, which host some of the most productive soils in the world, are particularly sensitive to changes in the dynamics of the water cycle. “We can still learn a lot from this. Many of the inhabitants of the plain live a few meters above the groundwater table, but most do not even know that it exists,” says the scientist. According to their study’s measurements, the groundwater level has risen from 12 to 6 meters below the surface to 4 to 0 meters today. This means a rise in water levels of 17 cm per year in various parts of the Pampas region.
“By changing the type of vegetation, we change the ability of the system to drain and dry the water,” says Jobbágy. Despite the severe drought that the region has been suffering from for years, the water cannot evaporate. “If we look at the records of the last few decades, it rains less than the sun can steal here, but the landscape keeps the water on the surface, which floods more and more often,” he explains.
A flood in an Argentine agricultural community. With kind approval
This phenomenon, about which so little is known, began with the “soy boom” that began in the mid-1970s and resulted in a predatory expansion of the country’s agricultural frontiers. Currently, the production of this grain occupies between half and two-thirds of the cultivated Argentine plain. “The rest consists almost entirely of corn cultivation, accompanied by wheat and barley, depending on the summer or winter season,” says Jobbágy about “an agriculture that has grown on a large scale and adapted to brutal capitalism.” There is still small producers who cultivate their small plots, but the large areas, sometimes hundreds of thousands of hectares, are in the hands of large companies.” The recent increase in the international price of wheat due to the war in Ukraine suggests that Argentina is increasing the area under cultivation for the in-demand product will continue to expand.
“We are talking about a country where there is hardly any spatial planning, hardly any regulation, and where lands are passed from hand to hand in a very violent way. Some federal states are discussing normative ideas in order to translate them into regulations, but these are only the first steps,” explains the scientist.
The results of their research show the escalation of flooding associated with the expansion of rain-fed agriculture in South America and the impact of rising groundwater levels, “but its impacts and risks are still poorly understood and pose major challenges for sustainability,” he warned.
To stop the system’s increasing instability, the study, which has been under way for years, calls for urgent implementation of land use policies that support agriculture, water management and rural populations in smarter ways. “And that they also integrate the conservation of what little nature we have left, these small patches of forest, wetlands and grasslands,” says Jobbágy.
According to the scientist, social and environmental justice are completely intertwined in the agricultural landscape of the Argentine plain. “That brings with it a lot of challenges. “We are a country that practically lives on grain exports, and these hydrological changes can endanger the good life of the territory and its people,” says the author of the study published in June.
His conclusion: The results of the work offer the opportunity to better understand the effects of converting natural landscapes into arable land and their hydrological effects underground. Also for designing policies that help find balance in the ecosystem. “We have changed the way the plain stores and transports water, creating an unknown creature that began waking decades ago and cannot easily go back to sleep. Only with good agreements will we learn to live with it.”