For the last 100 years, an ongoing study has looked at river levels in the Amazon and the frequency with which the world's largest river floods. The most recent information shows that the river is five times more prone to flooding than when the study first began. Scientists are looking at the potential causes of the increased flooding, which could lead to more accurate predictions and advanced warning for those who live in the Amazon Basin.
For 113 years, water levels have been recorded every day in the Brazilian city of Port of Manaus. In the past twenty to thirty years, the records have shown a substantial increase in the number of severe floods and droughts. When the study first began over a century ago, severe flooding with water levels in excess of 95 feet (29 meters) occurred about once every 20 years. Now, those levels are achieved about once every 4 years.
A recent study conducted by the Universidad Austral de Chile suggests that the increased frequency of the floods could be the result of the something called the Walker circulation. This phenomenon is driven by changes in air pressure and temperatures over the oceans. These pressures and temperatures drive the rainfall over tropical areas and specifically, the Amazon Basin.
In short, the Atlantic has been getting warmer and Pacific has been getting cooler, which draws a LOT of precipitation in the Amazon. What remains unclear is what is causing the temperature fluctuations, though global warming is at least partially responsible.
Ultimately, the goal is to use the research data to come up with a better way of warning those in the Amazon basin who live on and earn their livelihood from the river. In periods of extreme flooding, the effects can be catastrophic for the residents. Water supplies get contaminated, spreading disease. Floods destroy homes and businesses like cattle farming and agricultural activities.
Unfortunately, all evidence points to the Atlantic continuing to warm at a much higher rate than the Pacific, suggesting that the flooding will continue to increase in frequency over the next several years.