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Farming Fuels More Floods in South American Plains

by Graeme Hammer
Farming Fuels More Floods in South American Plains

The vast and rich grasslands of South American Pampas are dealing with a major problem. In the past half-century, this region has experienced severe floods that destroyed many crops, caused damage to roads and structures, and forced people to leave.

Scientists looked into this and discovered that farming is making the floods worse. As farmers expand their fields to grow more crops, the floods are also getting larger. In the last 40 years, the flooded areas have doubled in size.

Javier Houspanossian, who looked into this, explained that floods happened sometimes before. But when new floods came, areas that normally didn’t get flooded were also affected. He is part of a team that studies the environment in Argentina.

The Pampas cover parts of Argentina, Brazil, and Uruguay. They have the Andes mountains on one side and the Brazilian highlands on the other. There are big cities here, and the soil is great for farming. The soil can drink up rain and doesn’t need extra water from people. This is why a lot of soybeans and corn are grown here. But because of that, about 16% of the original plants have been removed in the last 20 years.


In a new study that was put in the Science journal, researchers looked at pictures from satellites, information about water below the ground, and things they learned when they went to the fields. They also used computers to help them understand why there are more floods happening in the flat areas of South America.

After looking at data from satellites, scientists found out that the Pampas region has been facing worse floods than other parts of the continent. This began around 1977. The areas that are getting flooded are moving to the very flat places where there are many crops.

When the 21st century started, farming in this area grew a lot and became more powerful. During this time, floods started happening in spots that never really had floods before. After this time, more than three out of every four new flooded spots on the continent were in these flat areas.

Information from eight monitoring spots in the Pampas region tells us that the water underground has shifted. In the 1970s, it used to be deep down (between 6 to 12 meters), but since the 2000s, it has come closer to the surface (between 0 to 4 meters), especially in places where people are growing crops.


After looking at the fields and using computers to try to figure out what’s going on, they found explanations for both the floods and the rising water underground. It seems that changing the natural plants to crops is making the area more likely to get flooded. The crops don’t have long roots like the grasslands and forests that were here before. Because of this, the Pampas can’t absorb and hold water like it used to.


Flood-Fighting Plants

Plants use their roots to drink water from the soil. They release this water into the air as vapor through a process called transpiration. When plants have long roots, they can pull water out of the ground effectively.


The Pampas is very flat, so when it rains, the water doesn’t spread out much. Instead, it goes into the ground sideways and gathers below. The plants that naturally grow here can send their roots really deep, about 15 meters, to reach this water. But crops, like soybeans and corn, have shorter roots, around 3 meters deep.

They can only get water from closer to the surface. Plus, crops only grow for part of the year, so they can’t drink up water all the time like the natural plants can.

“Think of it like a bank: The old plants with long roots can take water out well, but crops with short roots and breaks in planting can’t do that as well,” explained Bridget Scanlon, a water specialist from the University of Texas at Austin. “This causes water to gather, and the level of water underground rises, which leads to floods.”

Scanlon, who wasn’t involved in the new research but studies how land use affects water underground, was amazed by how big the problem is in the Pampas. Similar situations have been observed in places like the United States and South Africa, she pointed out. However, nowhere else has experienced floods to the extent seen in the Pampas.

Great for Plants, but Not Forever

Seeing the bright side, the researchers also found out (in another study) that the water underground rising in the Pampas could be helpful for farming by shielding against the problems of dry periods. Yet, they stressed that this good effect will only last for a short time.

The authors are advising that the risk of floods in the Pampas will keep growing as more crops are put in and the effects of climate change, like more rain, begin. “We won’t need a very big amount of rain to get more floods,” Esteban Jobbágy, a coauthor and geoscientist at CONICET, explained. “There won’t be adequate space to manage the extra water, particularly during the summers in the upcoming years.”

Other than the immediate problems from floods, the water below the ground has lots of salts. These salts go onto the top of the soil over time and that’s not good for farming. As the floods get worse, the bad effects of the soil getting salty could become more important than the short help it gives during dry times, as the researchers explained.

Realistic Ways to Help

Basic Ideas Bring Hope. Farmers can try planting different kinds of vegetables that have long roots, such as vetch and rye, to change the crops over time. Another option is to grow trees or pastures, which naturally drink up more water from the ground and help keep the water level lower, the researchers suggested.

Making sure farmers have the correct tools to keep an eye on the water underground is also important. This way, they can change their crops and get ready for floods. Jobbágy and Houspanossian are working on a project right now to create cheap tools that connect to smartphones and can measure how much water is in the ground.

“If farmers can watch the water level and use that information to decide how to use their land, considering the chance of floods, they will do better,” Houspanossian said.

However, Jobbágy emphasized that the ultimate decision rests on politics and relies on choices made by the government about how the land should be used. “While it’s nice that we can somewhat manage things by watching the water underground, the tricky part is figuring out who gets to decide what the right water level should be in different places,” he explained. “That’s why having rules about how the land is used is really crucial.”

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