Rainy Carnival in Rio and Sao Paulo
The weather system that scorched São Paulo has dissipated. Rain fell there and in Rio during the recent Carnival celebrations, and more is likely in weeks ahead.
That’s the good news.
The bad news is that the rainy season usually ends in April, so many more dry months lie ahead that will shrink the water supplies even more.
Still the water level in the main reservoir system is at 6 percent of its capacity: a record low. Boom-and-bust water phenomenon could become a new normal in South America, scientists say.
Marengo, senior scientist at the Brazilian National Center for Early Warning and Monitoring of Natural Disasters: “It’s like a seriously ill patient who is now a little less seriously ill.”
Scientists not really understand the boom-and-bust cycle, but meteorologist José Marengo says it has been triggered by a sprawling high-pressure system that settled stubbornly over southeastern Brazil. That region is usually at the end of a long loop of moisture-bearing trade winds. Last year, however, this system went awry.
The loop starts in the Atlantic Ocean, where the winds carry moisture westward over the Amazon. Some falls as rain, but as the air passes, it also absorbs moisture from trees. When these “flying rivers” hit the Andes, they swing south, showering rain over southeastern Brazil.
In 2014 however, a phenomenon called “atmospheric blocking” transformed that wind pattern.
- There was a giant bubble that deflected the moisture-laden air, which instead dumped about twice the usual amount of rain over the state of Acre, in western Brazil, and the Bolivian Amazon.
- At the same time, cold fronts from the south, which cause precipitation over São Paulo and Rio de Janeiro, were shunted aside, and as the system lingered, the drought took hold.
Scientists aren’t sure what caused the atmospheric blocking to linger over southeastern Brazil.
“it could be a sign of what lies ahead if temperatures continue to rise as projected,” Marengo said.