A team of international scientists found that El Niño—a natural warming of the central Pacific that changes weather worldwide—doubled the likelihood of the low precipitation Panama received during last year's rainy season. That dryness reduced water levels at the reservoir that feeds freshwater to the Panama Canal and provides drinking water for more than half of the Central American country.

Human-caused climate change was not a primary driver of the Central American country's unusually dry monsoon season, the World Weather Attribution group concluded, after comparing the rainfall levels to climate models for a simulated world without current warming.

The study has not been published in a peer-reviewed scientific journal yet but follows scientifically accepted techniques, and past such studies have frequently been published months later.

"Natural variability plays a critical role in driving many extremes," said Kim Cobb, a climate scientist at Brown University, who was not involved in the study. "This is an important reminder that climate change isn't always the answer."

Panama experienced one of its driest years on record last year, receiving below-average rainfall for seven of the eight months of its May to December rainy season.