There has been much discussion about the role that climate change may have played in the terrible fires that are devastating the Los Angeles area. Almost as if on purpose, in recent days a study has been published in the journal Nature Reviews earth and environment which details the climatic mechanism that is fueling the fires of recent weeks: it is the hydroclimate whiplash, or “hydroclimatic whiplash”. , a phenomenon linked to the increasingly higher temperatures reaching our atmosphere, and therefore – pace the deniers – increasingly frequent due to global warming.
The whiplash
The situation that California has experienced in recent weeks is somewhat paradoxical. The Los Angeles area is in fact no stranger to periods of intense drought, which can create the perfect conditions for the spread of flames. But in the last two years, both the winter of 2022 and 2023 had been particularly rich in precipitation. A particularly hot summer, and a dry winter this time, have therefore created what climatologists call hydroclimate whiplash: a sudden change from conditions of great humidity to periods of intense drought.
Speaking of fires, this is the worst case scenario: two years of rain and snow had in fact led to a lush growth of vegetation, which then dried up with the sudden arrival of the arid climate, and provided abundant fuel for the flames of these weeks. As we were saying, it is a situation that – explain the authors of the new study – is becoming more and more common throughout the world, and will only get worse in the future, because it is fueled by the increase in temperatures caused by global warming.
An atmospheric sponge
In the study, researchers from the University of California at Los Angeles reveal that hydroclimatic whiplash has increased in frequency by between 31 and 66 percent compared to what was still happening in the middle of the last century. More than was predicted by the most used climate models. And this – they explain – because in the past attention was paid to only one of the variables at play, namely the arrival of dry periods in which rainfall is absent, neglecting another mechanism which can significantly speed up the drying out of the soil, namely the Accelerated evaporation caused by the increase in air temperature.
The warmer the air – in fact – the more water it can hold. When the atmosphere increases in temperature, the humidity it draws from the soil and vegetation through evaporation also increases. And in the absence of rain this causes drying up much more rapidly than what would be seen if the air temperature were lower. The effects are dramatic: for every additional degree that our planet’s atmosphere gains, its ability to absorb water increases by 7%.
“This continuous expansion of the sponge effect of the atmosphere may be the explanation for some of the most evident, and dramatic, consequences of climate change that seem to be accelerating in recent years,” underlines Daniel Swain, climatologist at the University of California at Los Angeles who collaborated on the study. “The planet is warming basically at a uniform pace, but in the last five or 10 years there has been a lot of discussion about how the consequences seem to be accelerating. This increase in hydroclimate whiplash, mediated by the expansion of the atmospheric sponge, provides an extremely compelling possible explanation.”