The study finds that the drought that the Panama Canal thickened was linked to El Nio

The recent drought in the Panama Canal was not driven by global warming but by below-normal rainfall linked to the natural El Nio climate cycle, an international team of scientists has concluded.

Low reservoir levels have slowed cargo traffic in the canal for most of the past year. Without enough water to raise and lower ships, officials last summer had to cut the number of ships they allowed through, creating expensive headaches for shipping companies around the world. Only in recent months have crossings started to pick up.

Areas of concern for water could still deepen in the coming decades, the researchers said in their analysis of the drought. As Panama’s population grows and maritime trade expands, demand for water is expected to be a much larger proportion of available supply by 2050, according to the government. This means that future El Nio years could bring even greater disruptions, not only to global shipping, but also to water supplies for local residents.

Even small changes in precipitation can have disproportionate impacts, said Maja Vahlberg, a risk consultant at the Red Cross and Red Crescent Climate Center who contributed to the new analysis, which was released Wednesday.

Panama, in general, is one of the wettest places on Earth. On average, the area around the canal receives more than eight feet of rain a year, almost all of it during the wet season from May to December. This rain is essential both for the canal’s operation and for the drinking water consumed by half of the country’s 4.5 million people.

Last year, however, rainfall was about a quarter below normal, making it the nation’s third driest year in nearly a century and a half of records. The drought came shortly after two others that also hampered canal traffic: one in 1997-98, the other in 2015-16. All three matched the Nio’s conditions.

“We’ve never had a cluster of so many really intense events in such a short time,” said Steven Paton, director of the Smithsonian Tropical Research Institute’s Physical Monitoring Program in Panama. He and the other scientists who conducted the new analysis wanted to know: Was it just bad luck? Or was it related to global warming and therefore a harbinger of things to come?

To answer the question, the researchers looked at both Panamanian weather records and computer models that simulate the global climate under different conditions.

The scientists found that low rainfall, not high temperatures causing more water to evaporate, was the main reason for the low water in the canal reservoirs. Weather records suggest that wet season rainfall in Panama has declined modestly in recent decades. But the models do not indicate that human-induced climate change is the driver.

“We weren’t sure what was causing this slight drying trend, or whether it was an anomaly or some other factor we didn’t account for,” said Clair Barnes, a climate researcher at Imperial College London who worked on the analysis Future trends in a warming climate are also uncertain.

El Nio, by contrast, is much more clearly linked to below-average rainfall in the area, the scientists found. In any El Nio year, there is a 5 percent chance that rainfall will be as low as 2023, they estimated.

At the moment, conditions in El Nio are weakening, according to the National Oceanic and Atmospheric Administration. La Nia, the opposite phase of the cycle, is scheduled to appear this summer.

The scientists who analyzed the Panama Canal drought are affiliated with World Weather Attribution, a research initiative that examines extreme weather events shortly after they occur. Their findings on drought have not yet been peer-reviewed.

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