Scientific American: Rain began to fall over the Argentine capital of Buenos Aires late at night April 1. By the next morning, rainfall records for the month had been broken and the city woke up to find its streets covered with water.
Torrential rains dumped more than 6 inches of water on the city in less than two hours, according to reports from the Buenos Aires Central Observatory, killing eight people and leaving hundreds displaced. But the worst was yet to come.
The next night through April 3, a second storm poured more than 7 inches near the airport in the city of La Plata, 34 miles southeast of Buenos Aires. Local news outlets reported 11 to nearly 16 inches in precipitation in some localities in La Plata.
Images of washed-up vehicles, half-submerged living rooms and businesses, and people waist deep in water or moving around in paddle rafts were plastered all over the media, along with reports of power outages, severe interruption in transportation systems and tragedy. The official death toll in La Plata closed at 51, with one missing person and more than 1,500 evacuees, said the Argentine Ministry of Justice and Security of the province of Buenos Aires.
Damage in La Plata alone was around $500 million, according to preliminary estimates.
“It’s the biggest climatological disaster in the history of the city [of La Plata],” Minister of Justice and Security Ricardo Casal said in a statement.
So what happened?
Frequency of extreme rain events ‘has tripled’
Argentina’s official rainy season spans from December to March, during the austral summer, with an average of 100 millimeters (just shy of 4 inches) of rain a month. But in the last couple of years, the development of big offseason storms is becoming something of a new normal.
The extreme weather events experienced by the cities of La Plata and Buenos Aires at the beginning of April coincided with a pronounced trend observed over the last three decades in the region known as “Wet Pampa” — which sprawls south from Brazil to south of the Buenos Aires province — explained Pablo Canziani, director of the Interdisciplinary Team for the Study of Atmospheric Processes in Global Change of the Pontifical Catholic University of Argentina.
“Since the early ’80s, the frequency of extreme weather events dumping over 100 millimeters of water has tripled,” Canziani said.
According to the National Meteorological Service (SMN) of Argentina, from 1961 to 2010, the average annual precipitation has increased in almost the entire country, particularly in the Argentine littoral — the region between the Paraná and Uruguay rivers in the northeast — the region of Cuyo, and the center and north of the country.
Although torrential storms aren’t uncommon in the Buenos Aires region, the issue is that they are becoming more frequent, Canziani said. And by the looks of it, it’s going to get worse.
Based on global models by the Intergovernmental Panel on Climate Change, between 2020 and 2029, central and eastern Argentina will see a 2 percent to 8 percent increase in rain, while precipitation levels will drop 2 to 12 percent in the northwest, information by the SMN showed. Average temperatures are expected to rise throughout the entire country by 0.7 and 1.2 degrees Celsius, with the highest temperatures projected for the northeast.
Why cities get overwhelmed
Yet climate change is only partly to blame.
The amount of water brought on by the April storms would have probably flooded even the best-drained city, Canziani said. But the situation becomes much worse when such downpours take place over large urban areas — with asphalt and cement making it almost impermeable — combined with poor planning, as is the case for Buenos Aires or La Plata, he said.
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