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Is global warming bringing more rain?
Devastating storms and heavy rains seem to be inundating the world with ever greater frequency.
A study published on July 6, 2021 has recently confirmed what we have long suspected: human activity is accelerating global warming and causing increasingly heavy precipitation. Whether in the form of rain, hail or snow, this precipitation leads to floods, landslides, agricultural losses and other damage all over the world. Several countries suffered the consequences of this phenomenon last summer, from Germany and Russia to Japan and the United States.
Rare and limited data
Climate models allow us to reproduce and eventually predict climate patterns using a broad range of equations. Computer models like these have long predicted that intense precipitation events would occur with greater frequency as the planet gets warmer. "As the air warms up, the amount of moisture it can hold increases. So when a storm forms, there is more water vapor available in the atmosphere and precipitation is heavier," explains Gavin D. Madakumbura, lead author of the study and a hydroclimatology researcher at the University of California (UCLA). And since climate change is affecting the planet's major hydrologic cycles, the gap between the two extremes is also likely to widen: on the other end of the spectrum, droughts are becoming longer and more intense.
“As the air warms up, the amount of moisture it can hold increases. So when a storm forms, it has more water vapor available in the atmosphere and precipitation is heavier”
In practice, however, the actual role of climate change in triggering these extreme rainfall events has remained difficult to determine. "Previous methods required extensive databases covering several decades. But these data are rare and limited to certain regions," says Gavin D. Madakumbura. In addition, much of the available data has been recorded through different and inconsistent methods, which has given rise to many uncertainties.
“An anthropogenic signal”
To overcome these challenges, researchers used an artificial intelligence method called "machine learning": this type of computer program can teach and train an "artificial neural network" that mimics a human brain. After receiving training on climate models, the program sifted through global precipitation records from 1982 to 2015. The conclusion: the frequency of extreme precipitation events closely matches the predictions of models that account for global warming.
As the researchers summarize, the study detected "an anthropogenic signal in global extreme precipitation", and this factor is clearly distinct from natural climate variation. “The human influence we detected relates to global warming as a whole, without distinguishing between the various contributing activities," says Gavin D. Madakumbura. “We might think of aerosols or changes in land use [with deforestation or urbanization, for example], but greenhouse gas emissions are the main cause."