New data suggest that flooding in the Amazon River has dramatically increased by as much as five times in both intensity and frequency in the last 100 years. Scientists analyzed data points from the past century and believe the increase in flooding is linked to global warming.

Scientists have measured the river’s water levels for 113 years at the Port of Manaus in Brazil. Over time, they found that large flooding events and extreme droughts have gone up over the past 20 to 30 years. In the early part of the century, massive floods only happened about once in every 20-year period. That number has increased to one major flood every four years.

Related: High tide coastal flooding in US has doubled in the past 30 years

The researchers believe the uptick is related to an oceanic system called Walker circulation, which describes air currents created by temperature fluctuations and pressure changes in the ocean, specifically in tropical locations. The Pacific Ocean has been cooling while the Atlantic Ocean has been getting warmer, which creates these circulating air currents. These changes are affecting the surrounding environment, including precipitation in the Amazon basin.

cropped close-up of water marks of flooding in the past 100 years at the Manaus Port

Scientists are not sure why the Atlantic Ocean has been warming up. They do, however, believe that global warming is contributing to the temperature changes, but in a more indirect way. They theorize that global warming has shifted wind belts farther south, which pushes warm water from the Indian Ocean to the Atlantic. This creates an opposite effect of El Niño and results in more rainfall in the Amazon.

Flooding along the Amazon River lasts weeks on end. Not only does it spread disease and contaminate water supplies, but it also destroys farms and homes.

Right now, there is no indication that the flooding will decrease. This past year, water levels rose above the flood range, and scientists believe the water levels will only get higher as the years progress.

Via EurekAlert!

Images via Dave Lonsdale and NASA