In a recent study, scientists found evidence that long-term changes in tropical weather patterns are leading to more frequent weather extremes in the Indo-Pacific. This region is particularly vulnerable to the effects of climate change, being home to over a billion people, as well as unique and vulnerable ecosystems.
Cambridge geophysicist Adriano Gualandi collaborated with a multidisciplinary team of climate scientists and engineers on the study, which was published in Nature Geoscience.
The research team, led by the National University of Singapore, examined decades of weather observations, finding that atmospheric conditions that were common in the past are now becoming rare, and new emerging weather patterns are associated with more frequent extreme weather events.
Climate science is a relatively new field to Gualandi, “typically I study the solid Earth rather than the atmosphere.” But, he explained, the maths governing aspects of recurring natural phenomena, such as earthquakes and weather extremes, share some similarities.
Both earthquakes and severe weather are controlled by nonlinear dynamics, Gualandi said, meaning that small perturbations to the state of a system can lead to very different evolutions.
Both systems are externally driven and dissipative. In the case of earthquakes, the movement of tectonic plates and friction on faults are the driving and dissipative mechanisms, with perturbations in Earth’s stress field causing earthquakes to happen with greater or lesser regularity. In the atmosphere, solar radiation is a driving mechanism, and turbulence caused by friction can change how heat energy gets distributed, influencing the resulting weather.
Nonlinear systems aren’t totally unpredictable though, and that’s one reason we can make weather forecasts. Edward Lorenz, father of chaos theory, first devised analogue weather forecasts in the 1960s. By comparing atmospheric charts through time, he found it possible to understand how similar ‘analogue’ conditions might manifest as different weather.
“You can start to predict these different outcomes, that is one possible way to make weather forecasts,” Gualandi said. Back in the ‘60s, Lorenz was working with minimal observations, describing “numerous mediocre analogues but no truly good ones," in his 1969 study. But, said Gualandi, “we now have more abundant data and can start using analogues more effectively.”
Gualandi and his colleagues used the same analogue concept to look at weather extremes. They found that specific atmospheric conditions were more likely to be associated with extreme weather over time. They also observed new emerging atmospheric patterns which seem to be more frequently associated with extreme weather, namely heatwaves and heavy rainfall.
These emerging weather patterns manifest as a stronger Pacific Walker circulation (or Walker cell) and are associated with wetter and warmer conditions in Southeast Asia and drier conditions in the equatorial Pacific.
According to Gualandi, their research could help anticipate when severe weather might be more likely, “this gives us an idea that, if we can identify the right patterns for extreme weather, we might have a way to forecast when they could happen and with which probability.”
Gualandi has already applied a similar analogues approach to earthquakes. The challenge with earthquakes, he said, is that they often have recurrence times of centuries, or even thousands of years. And, because seismologists have only had dense seismic arrays and geodetic networks since the 2000s, they don’t have enough recorded earthquakes to use as analogues. Instead, Gualandi has been studying slow earthquakes, which don’t cause shaking because they spread their ruptures in slow-motion; over the course of days to months rather than minutes. “Because slow earthquakes have shorter recurrence times (of the order of months or years), we can find several analogues during the instrumental period and start to understand the conditions that lead to frictional instability.”
Reference: Dong, C., et al. (2024). Indo-Pacific regional extremes aggravated by changes in tropical weather patterns. Nature Geoscience, 1-8.