Source: Panama Canal Authority.
The Panama Canal depends on an ample supply of freshwater captured by its watershed and stored in retention reservoirs such as Lake Gatun, usually during the rainy season which is between May and December. A look at the precipitation trend underlines fluctuations around an average of about 2.6 meters (2634 millimeters) per year. Since 1950, 14 years have had precipitations outside one standard deviation (wetter or dryer years), which is 19.4% of the time. These deviations are normal and associated with the El Nino Southern Oscillation, which is a fluctuation in sea surface temperatures in the Pacific Ocean, resulting in seasons of higher (El Nino) and lower (La Nina) rainfalls. 2023 was a dryer year than usual, corresponding to a longer-than-usual La Nina event.
There have been several prior occasions when rainfall was less than usual without noticeable enduring impacts on canal operations. The main reason the 2020-23 La Nina event restricted the availability of water for canal operations is related to the 2016 canal expansion, which created an additional set of locks that were much bigger than the old locks. Even if additional reservoir capacity was provided and the new locks had water-saving features, the restrictions on canal operations in terms of the number of transits per day and ship capacity underline the vulnerability of the Panama Canal to seasonal variations in precipitation, even without strong outliers events.
To mitigate this risk the Panama Canal Authority plans to extend the watershed supplying the canal so that it is less prone to fluctuations in water availability.