More drought, more flooding …
The Pacific Ocean’s El Niño-La Niña cycle may become a dominant factor in West Coast weather by the end of this century and lead to more frequent weather extremes, according to a new study published in Nature Communications. Based on the findings, California could see the number of extreme droughts and floods by 2100, the researchers found.
A better understanding of what gives rise to El Nino and La Nina cycles — together known as El Nino-Southern Oscillation — might help California predict and prepare for more frequent droughts and floods in the coming century.
“Wet and dry years in California are linked to El Nino and La Nina. That relationship is getting stronger,” said atmospheric scientist Jin-Ho Yoon of the Department of Energy’s Pacific Northwest National Laboratory. “Our study shows that ENSO will be exhibiting increasing control over California weather.”
The models developed for the study show that, in the future, assuming emissions continue to increase, California seasons will exhibit more excessively wet and excessively dry events. These results suggest that the frequency of droughts could double and floods could triple between the early 20th century and late 21st century.
“By 2100, we see more — and more extreme — events. Flooding and droughts will be more severe than they are currently,” said Yoon.
But why? Yoon suspected the El Nino-Southern Oscillation. Every two to seven years, El Nino comes in and warms up the tropical Pacific Ocean a few degrees, increasing winter rain and snowpack in California. On a similar schedule, La Nina cools things off. Both disrupt regular weather in many regions around the globe.
To explore El Nino’s connection to California precipitation, Yoon and colleagues ran a climate model with and without El Nino. In both simulations, they ramped up the concentration of carbon dioxide by 1 percent every year for 150 years. In just one of the runs, they removed El Nino’s cyclical contribution by programming the sea surface temperatures to reflect only steady warming.
Without El Nino and La Nina, the frequency of extreme precipitation in California stayed constant for the simulation’s century and a half. With ENSO, simulated California experienced wide swings in rainfall by the end of the period.
The results suggest that even though researchers expect rain and snowfall to increase as the climate warms, the manner in which the water hits California could be highly variable.