How El Niño could reshape monsoon season around the world
El Niño has often been linked with weaker monsoons—but experts warn this year has the potential to be unpredictable.
It's becoming increasingly likely that this year will bring a powerful El Niño. And the first test of how strong it really is could come as soon as early June with the arrival of monsoon season. Experts warn that the weather system emerging in the Pacific Ocean could upend the typical precipitation patterns of monsoon seasons in much of the world.
(What a 'super' El Niño means for the planet.)
El Niño—a long-recurring phenomenon that takes place about every two to seven years—is known for changing Earth’s atmospheric moisture flows, causing drought in some places and heavy rainfall in others. In the past, El Niño has been linked with weaker monsoons, dry seasons, and crop failure. But scientists say the weather pattern can also yield unpredictability, with less overall precipitation but more extreme rainfall events.
And El Niño can be influenced by the conditions that came before it.
“What happened in the winter and into the spring is actually just as important—if not more important—than the monsoon season itself,” says Jon Gottschalck, chief of the operational prediction branch at the National Oceanic and Atmospheric Administration’s Climate Prediction Center.
The powerful phenomenon brewing in the Pacific could bring food insecurity, drought and fires to places that usually start to see steady rain this time of year. In the American Southwest, which saw a dry and warm winter, the monsoon could still be powerful, with heavy, hazardous rain.
What is a monsoon?
A monsoon is a seasonal shift in winds that technically occurs in the winter and summer, when temperature differences between the land and the ocean push either rain or dry air to land. The term is most used to refer to summer rainy seasons, when sea air travels inland, condenses, and turns into humidity and persistent rain.
Most tropical landmasses, including parts of West Africa, East Asia, Australia, and even the American Southwest experience some form of wet monsoon during local summer.
The biggest and most famous monsoon is in India, and accounts for 90 percent of total annual precipitation in some parts of the country.
How could an upcoming El Niño influence this year’s monsoon?
When faced with one another, El Niño and monsoon season jockey for control of the sky’s moisture buildup.
El Niño occurs when the central and eastern equatorial Pacific Ocean warms, reshaping atmospheric patterns across the whole planet. The warmer water pulls rainfall toward that patch of sea—away from other parts of the world, says Spencer A. Hill, an assistant professor at the City College of New York, who researches the dynamics of Earth’s monsoons.
Typically, El Niño dries out parts of the planet, bringing less rainfall and warmer temperatures to places including the Caribbean, Indonesia, and Australia.
India in particular sees less rainfall during El Niño summers. Already, the country’s meteorological department has forecast a below normal monsoon season, adding that it was carefully monitoring sea surface temperatures in the Pacific.
But it’s not as simple as how much precipitation occurs.. Hill and other researchers concluded that while total rainfall consistently declines in India during El Niño, extreme rainfall paradoxically increases.
In a short time scale, “way too much rainfall could be devastating,” says Hill, causing landslides and floods especially in a place that’s experiencing dry weather that yields loose, brittle soil.
And El Niño doesn’t happen in a vacuum. In another twist, the warm winter and spring that took place in the American Southwest could strengthen the monsoon season there even with El Niño’s dampening effects.
“Since it was so dry and there’s no snow, the land is likely going to be heating up quicker, more intensely,” says Gottschalck. “And that could mean very strong monsoon circulation potential.”
For India, less snow cover in the Himalayas can bring a stronger monsoon, even in El Niño years.
The location of El Niño’s warming is also critical to the strength of monsoons—if it’s further east in the Pacific, it could have less of an effect on India’s monsoon.
But “right now it looks like it’s going to be basin-wide event,” says Gottschalck, meaning the warming will probably affect monsoon systems in India, Indonesia and West Africa.
Gottschalck notes it takes time for higher latitudes to feel the effects of El Niño. In the tropics, the impact is faster.
What are the widespread impacts of El Niño?
Scientists stress that it’s too soon to say how strong this El Niño will be, and how its forces will converge with other weather conditions to affect forecasts.
But hotter and dryer summers, as well as the extreme rainfall events associated with the phenomenon, can devastate crops and the people who grow and eat them.
“If you have rainfall that you can expect to continue over the whole season, all your options remain open,” says Gottschalck. But “when there’s a more erratic monsoon, it really increases a tremendous uncertainty in the water resource and agricultural management.”
Crops can start off well and then be completely dried out by the end of the season or washed away. On the flip side, you could have so much rainfall and flooding at the start of the season that it delays the planting of crops.
In 1983, a weak monsoon linked with El Niño contributed to the largest worldwide crop failure in modern history, scientists found.
Drier summers can also lead to wildfires, heat waves, and the health hazards they bring. And they upend the semiannual rhythms that define industry and life in so much of the world.
“It’s going to be a very rough period,” Gottschalck says. “Right now it looks like there will be considerable negative impacts in many of the tropical monsoon regions across the globe.”
