Flood causing logistical problems.
Newswise — Researchers emphasize that a recent study exposing the detrimental effects of extensive large-scale agriculture on the South American plains should serve as a crucial wake-up call. Over the past few decades, the grasslands of the Argentinean Pampas and other vast flat regions in South America have undergone substantial and rapid transformations. The soaring global demand has driven the conversion of expansive grasslands and forests into the production zones for annual crops like soybean and maize. Shockingly, this agricultural expansion has been occurring at an alarming rate of 2.1 million hectares per year.
While concerns about biodiversity and soil degradation resulting from these changes have long been recognized, a new scientific study, published in Science, highlights another critical issue. It reveals how the shift to rain-dependent annual crop agriculture is swiftly disrupting the water table across the vast, level areas of the Pampas and Chaco plains. Consequently, this disruption significantly heightens the risk of surface flooding.
A team of international researchers from the University of San Luis in Argentina and Lancaster University in the UK has utilized satellite imagery, field observations spanning four decades, statistical modeling, and hydrological simulations to unveil significant trends regarding groundwater and flooding. Their findings provide unprecedented evidence of how human-induced subtle alterations in vegetation cover can fundamentally transform the water cycle across expansive regions.
Dr. Javier Houspanossian from the National University of San Luis in Argentina commented, "The replacement of native vegetation and pastures with rain-fed croplands in South America's major grain-producing area has led to a notable surge in the frequency and extent of floods." He further stated, "High-resolution remote sensing imagery has captured the emergence of new flooded areas, expanding at a rate of approximately 700 square kilometers per year in the central plains—an unprecedented phenomenon on the continent."
The data revealed a concerning trend where the substitution of deep-rooted native vegetation and pastures with short-rooted annual crops is progressively amplifying the coverage of floods, rendering them more susceptible to precipitation fluctuations. Previously situated at considerable depths (12-6 meters), groundwater levels are now rising to shallower depths (around 4 meters).
Dr. Esteban Jobbágy from CONICET in Argentina explained the consequences of replacing deep-rooted vegetation with shallow-rooted annual crops on a vast scale, stating, "This widespread substitution has led to a rise in the regional water table, bringing it closer to the surface." As the water level approaches the surface, the land's capacity to absorb heavy rainfall naturally diminishes, thereby increasing the likelihood of flooding.
The flatness of the land plays a crucial role in this heightened sensitivity to shallower water tables since water flows very slowly in such areas. Coincidentally, these flat sedimentary plains often harbor some of the most fertile farming soils on the planet. Dr. Jobbágy emphasized the significant role of vegetation changes in these exceptionally flat regions, as plants possess the ability to draw down groundwater reserves during dry periods, thus modulating the occurrence of flooding.
The researchers view these findings as a vital wake-up call, illustrating how rapid agricultural expansion across extensive plains can disrupt hydrological processes on a large scale, consequently elevating the risks of flooding. Professor Mariana Rufino, formerly of Lancaster University, expressed concern over the impact of these floods not only on local farmers and residents but also on food supplies and prices, as further expansion of these floods could have far-reaching consequences.
"These findings should serve as a crucial wake-up call, emphasizing the potential risks associated with large-scale and rapid land-use changes in extensive flat landscapes, particularly concerning hydrological transformations," remarked the researchers.
In addition to the increased risk of flooding, these human-induced hydrological changes also pose threats such as soil erosion, methane emissions, and land salination due to salt accumulation.
The researchers argue that the hydrological shifts observed in the South American plains can provide valuable insights for similar flat regions undergoing agricultural intensification worldwide, including central Canada, Hungary, Kazakhstan, parts of China, and Ukraine.
Professor Peter Atkinson from Lancaster University commented, "This research serves as a reminder that our planet is a delicately balanced system, and our actions in one area can have unintended negative consequences in another, spanning vast geographical extents."
According to Dr. Wlodek Tych from Lancaster University, the research employed a statistical modeling approach that avoided bias and strong assumptions, thereby adding rigor to the findings that link the expansion of intensive agriculture to an increased risk of flooding. These findings should serve as a foundation for developing new land management policies across the expansive flat rain-fed regions.
The authors emphasize the pressing need for smarter land use policies that promote sustainable farming practices and well-informed water management strategies. Dr. Jobbágy suggests that allocating specific areas of land to deep-rooted forest patches and perennial pastures can effectively prevent the occurrence of very shallow groundwater. Other potential solutions include breeding crops with deeper root systems and implementing crop rotations that are adaptable to water table depths.
The findings, outlined in the paper titled "Agricultural expansion raises groundwater and increases flooding in the South American plains," published in Science, highlight the importance of proactive measures to mitigate the adverse effects of extensive agriculture on hydrology and flood risks.
The paper’s authors are Javier Houspanossian and Raul Gimenez of CONICET and the National University of San Luis, in Argentina; Juan Whitworth-Hulse and Esteban Jobbagy of CONICET; Marcelo Nosetto of CONICET and Universidad Nacional de Entre Rios; Wlodek Tych, Peter Atkinson and Mariana Rufino of Lancaster University.
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