The recent Panama Canal drought was not caused by global warming, but by below-normal rainfall associated with the natural climate cycle, El Niño, an international team of scientists has concluded.
Dropping water levels in the reservoir have slowed cargo traffic through the canal for much of the past year. There wasn't enough water to raise and lower ships, forcing authorities to cut back on the number of ships allowed through last summer, causing costly headaches for shipping companies around the world. It is only in recent months that the number of intersections has started to increase again.
In their analysis of the drought, researchers said water concerns in the region could deepen in coming decades. According to the Panamanian government, water demand is expected to account for an even larger proportion of available supply by 2050 as Panama's population grows and maritime trade expands. This means that future El Niño events could cause broader disruptions not only to global transportation but also to water supplies to local populations.
“Even small changes in precipitation can have disproportionate impacts,” said Maya Varberg, a risk consultant at the Red Cross Climate Center who contributed to the new analysis released Wednesday.
Panama is generally one of the rainiest places on earth. The area around the canal receives an average of more than 8 feet of rain per year, with most of it falling during the rainy season from May to December. That rain is essential both to the operation of the canal and to the drinking water consumed by about half of the country's 4.5 million people.
However, last year's rainfall was about a quarter less than normal, making it the third driest year in Japan in about 150 and a half years of record. A dry spell occurred shortly after two other disasters that similarly impeded canal traffic. One was in 1997-1998 and the other in 2015-16. All three times coincided with El Niño conditions.
“This is the first time we've seen so many very intense events come together in such a short period of time,” said Stephen Payton, director of the geophysical monitoring program at the Smithsonian Tropical Research Institute in Panama. He and the other scientists who conducted the new analysis wanted to know: “Was this just bad luck?” Or was it related to global warming and therefore a harbinger of things to come?
To answer this question, the researchers looked at both Panama's weather records and computer models that simulate Earth's climate under a variety of conditions.
Scientists found that the main reason for the decline in water in the canal's reservoirs was less rain, rather than higher temperatures that caused water to evaporate. Weather records show that Panama's rainy season rainfall has decreased slightly in recent decades. However, these models do not show that anthropogenic climate change is the cause.
Claire Burns, a climate researcher at Imperial College London who worked on the analysis, said: “I'm not sure what's causing that slight drying trend, or whether it's an anomaly or some other factor that hasn't been taken into account. We don't know.'' . “Future trends in a warming climate are also uncertain.”
In contrast, El Niño events are more clearly associated with below-average rainfall in the region, scientists found. Researchers estimate that in a year when El Niño occurs, there is a 5% chance that precipitation will be as low as in 2023.
According to the National Oceanic and Atmospheric Administration, El Niño conditions are currently weakening. This summer, the reverse phase of the cycle, La Niña, is expected to occur.
The scientists who analyzed the Panama Canal drought are part of World Weather Attribution, a research effort that investigates extreme weather events immediately after they occur. The results of the drought study have not yet been peer-reviewed.