Expanding agriculture could worsen flooding in South American plains, study says

International demand for soybeans and corn has turned the South American plains into an economic pillar for countries like Argentina, Brazil, Uruguay and Paraguay. But all of that activity also comes with a heavy price. A new study published last month in Science found that industrial agriculture is making the region more susceptible to “widespread flooding,” something researchers warned should serve as a wake-up call to farmers and lawmakers alike.

“These floods are a major concern for the farmers and people living in the region, but also elsewhere as further expansions of these floods could potentially disrupt food supplies and prices,” said co-author Mariana Rufino, a former professor at Lancaster University.

The South American plains — including Las Pampas and the Gran Chaco — have seen agricultural activity expand by around 2.1 million hectares (5.2 million acres) a year, according to a 2021 study on soybean expansion in the region.

Researchers used satellite imagery from the past four decades, statistical modeling and hydrological simulations to analyze shifting trends in the vegetation, revealing changes to the water cycle that could prove harmful to the entire region. Cropland for wheat, corn and cassava, among other things, has replaced native vegetation, resulting in new flooding — around 700 sq. km per year, the study said.

Groundwater that was once at a depth of around six-to-12 meters, is now rising to shallower levels, usually around four meters, the study said.

“By replacing deeper rooted trees, plants and grasses with shallow rooted annual crops over such a huge scale this has culminated in seeing the regional water table rise closer to the surface,” said Esteban Jobbágy, co-author and researcher with the National Scientific and Technical Research Council. “As the water level rises closer to the surface there is naturally less capacity for the land to absorb heavy rainfall, contributing to making flooding more likely.”

The study said that dedicating more space to deeper-rooted forests and perennial pastures — which grow year-round — could help prevent shallow ground water. It also suggested breeding crops with deeper root systems and developing crop rotations with more flexible water table depths.

The same lessons could be applied to other regions of the world with significant cropland increases, including Hungary, Kazakhstan and areas of China, the study said.

“These results should act as a wake-up call that if we are going to make such huge and rapid land-use changes across large flat landscapes then it can transform the hydrology with potential increased risks,” Rufino said.

Banner image: Las Pampas, Argentina. Photo: Wikimedia. 

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