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A vital waterway connecting the Atlantic and Pacific oceans, the Panama Canal relies on fresh water supplied by a reservoir to raise and lower the locks that allow the transit of thousands of ships a year.

During times of drought, fewer vessels make it through.

A new paper by Northeastern University professor Samuel Munoz reports that the risk of shipping disruptions will grow in a warming climate unless steps are taken to reduce greenhouse gas emissions or to adapt to drier conditions.

"The canal is vulnerable to drought. That vulnerability increases with climate change," he says. "The models think that the more we warm things, the more severe and frequent these droughts become in Panama."

The findings highlight the need to address a growing risk to a key link in the global supply chain with "proactive adaptation or mitigation" that maintains canal functionality, Munoz says in research in Geophysical Research Letters.

Water levels in the reservoir

For his study, conducted when he was on sabbatical in the spring, Munoz used high-resolution climate projections to simulate future levels of the feeder reservoir, Gatun Lake.

He found that "disruptive low water conditions" became increasingly common under moderately high and high greenhouse gas emission scenarios but not under low-emissions scenarios.

That is because Gatun Lake is fed primarily by rainfall, and higher emissions were associated with reduced wet season rainfall and increased evaporation.

"Every time a ship goes through, it uses a lot of water" through the flooding of locks to raise and lower ships as they cross the continental divide, says Munoz, associate professor of marine and environmental sciences and civil and environmental engineering.

"When they have droughts, the main thing that they can do is basically reduce the number of ships transiting through," he says.

Recent droughts, including one in 2023 and 2024, caused canal operators to reduce the weight and number of ships that cross the 50-mile-long waterway.

Reducing the impact of emissions

Using 27 different climate models and varying emission mitigation scenarios, Munoz predicted lake levels monthly out to the end of the century.

Mitigation means bringing down emissions and global temperatures.

"We looked at the rain coming in, we looked at how much water was evaporating away under these different scenarios.

"Under the scenarios where we don't mitigate emissions very much, the amount of rain that Panama gets goes down a lot and the amount of evaporation that occurs goes up a lot, so low lake levels become really problematic, really more common and severe than they are now," he says.

"But in scenarios where we do more mitigation of greenhouse gases, there's less change (in water levels) and it stabilizes more," Munoz says.

"Climate scientists look at a range of scenarios. Will we mitigate (emissions) really aggressively? It doesn't look like it," he says. "Will we not mitigate at all? Probably not. We're currently headed down one of the middle emissions pathways."

Adaptation and a new reservoir

For global and U.S. trade, the future of the Panama Canal is vitally important, Munoz says.

An average of 14,000 ships transit the canal annually, including 40% of U.S. container ships.

"If we're not going to mitigate emissions, then significant adaptation measures are needed to keep it functioning," Munoz says.

Panamanian authorities are looking to the future with plans to build a new reservoir to supplement Gatun Lake as well as finding ways to more efficiently use existing water supplies.

"They use the reservoir also for hydroelectric power for the country and drinking water for Panama City," so it makes sense to adapt to changing conditions, Munoz says.

Dealing with uncertainty

While the best climate models, including NOAA's Community Earth Systems Model, forecast drier conditions in Panama, there is still some uncertainty due to the local impact of the El Niño-Southern Oscillation.

The climate pattern involves surface ocean temperatures in the tropical Pacific and associated atmospheric circulation, Munoz says.

"This is a region of the world where climate scientists still aren't 100% sure exactly what will happen," he says.

"In Panama, canal authorities acknowledge there's uncertainty, but they are still moving ahead with these major investments to try to keep things stable," Munoz says.

"Smart management and mitigation are going to be key to keeping ships moving."