With plans for athletes to swim the Seine through the heart of Paris, Olympic organizers were essentially betting against the extreme weather of climate change. For days, it looked like they were going to lose, by scrapping the swimming portion of triathlon races.
It was only on Wednesday morning, after the men’s competition was postponed a day and test events were cancelled, that organisers announced that the most recent tests had shown the water met swimming standards.
Some scientists and engineers said the organizers were taking a big risk at a time when heavy rainfall has increased due to human-caused climate change, especially in Europe. The rainfall is draining away from urban areas and contributing to higher bacteria levels in the city’s famous river.
“They just took a chance, flipped a coin and hoped for a dry season, and it turned out to be the rainiest season in the last 30 years,” said Metin Duran, a professor of civil and environmental engineering at Villanova University who has researched stormwater management.
Organizers “had worked through most of the scenarios involving computer hacking and physical threats without fully assessing the implications of extreme events related to climate,” said Kathy Jacobs, a climate scientist at the University of Arizona and director of the Center for Climate Adaptation Science and Solutions. “It is absolutely time to take climate threats seriously.”
If there’s one city that might be expected to be aware of the challenges of climate change, it’s Paris. It’s where, almost a decade ago, the most important climate agreement in history was struck — to try to limit global warming to 1.5 degrees Celsius (2.7 degrees Fahrenheit) above pre-industrial levels. And the Paris Games are aiming to have half the carbon footprint of previous games in London and Rio de Janeiro.
Paris, like many older cities around the world, has a combined sewer system, meaning that the city’s wastewater and rainwater flow through the same pipes. When heavy or prolonged rainfall occurs, the pipes reach their capacity, causing raw sewage to be pumped into the river instead of into a treatment plant.
Paris spent 1.4 billion euros ($1.5 billion) to improve the water quality of the Seine. This included building a large basin to collect excess rainwater and prevent sewage from entering the river. It also renovated sewers and modernized water treatment plants.
But persistent rain, which dampened the opening ceremony and temporarily replaced a heat warning on Tuesday, worked against that. Tuesday’s men’s triathlon was postponed until Wednesday. The city has had at least 80 rainy days in Paris so far this year, about two and a half weeks more than normal, according to the French meteorological office.
An AP analysis of weather data found that Paris in 2024 will have the second-highest number of rainy days since 1950, surpassed only by 2016. There has been only one week of dry spell this year to give the drainage system a rest. Normally there would be at least three by then, the AP analysis found.
“Heavy rainfall in the summer has always been a possibility and with a warming climate these heavy rains have only become more severe, said Friederike Otto, a climate scientist at Imperial College London. “So that should certainly have been taken into account in the planning.”
A study last week in the journal Science found a striking global increase in the variability — the all-or-nothing quality — of rain and snow over the past 100 years, with a big jump starting in 1960. Researchers then ran standard climate attribution analysis to compare what actually happened with what would be expected in a fictional world without human-caused climate change. They found that this increase in heavy rain, punctuated by longer dry spells, bore the fingerprints of global warming.
The study also found that three areas – Europe, eastern North America and Australia – had seen much higher jumps in increases in extreme rainfall.
Peili Wu, a climate scientist at the British Meteorological Office and co-author of the study, said the laws of physics dictate that warmer air holds more moisture, which means heavier rainfall. But climate change is changing weather patterns, making downpours or sunny days without clouds more common.
Organizers said what happened was beyond their control. Aurélie Merle, the sports director of Paris 2024, noted to reporters on Tuesday that previous triathlon events had sometimes been reduced to duathlons. That was before Wednesday’s early announcement that the Seine swim would go ahead.
Duran, the Villanova professor, noted that the acceptable pollution level for the triathlon is nearly four times lower than the U.S. Environmental Protection Agency’s standard for swimming waters. The mayor of Paris made a public show of swimming in the river earlier this month, something Duran called a publicity stunt. He said he would not swim in the Seine.
He called the underground storage basins “the last thing a stormwater expert would propose as a solution,” Duran said. Few cities use that solution anymore because it is limited and easily overwhelmed by the heavier, more frequent rains of climate change. It’s a solution for the era before global warming hit hard, he said.
Villanova’s Duran said future Olympic venues must anticipate a wetter world: “The problem of sewer overflows will only get worse until something is done about climate change.”
According to Otto of Imperial College, Los Angeles, the host city for the 2028 Games, could learn a lesson from this and create more green spaces and fewer private vehicles.
“The Olympic Games are a great opportunity to change cities, because for some reason people accept that athletes need a healthy environment, while ordinary citizens have to live in an environment with pollution, traffic, noise and risk their lives and health,” Otto said.
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