More and more often, it burns longer and more intensely: A study now shows an important factor in the increase in the global threat of forest and bush fires: The warmer and drier nights as a result of climate change are literally fueling the trend. Satellite data shows that the intensity of nighttime fires has increased in recent decades. In addition, the corresponding fire-promoting conditions are more common in the endangered regions at night. The researchers say that firefighters will have to adapt more and more to round-the-clock operations.
Devastating seas of flames that burn forests and bush landscapes to ashes and also spread to settlement areas: As is well known, a particularly large number of violent fires have afflicted various regions of the world in recent years. Ecosystems and human livelihoods went up in flames, and much previously bound carbon was released into the atmosphere. The intensification of the threat from fires is mainly attributed to climate change. Higher temperatures and droughts are known to favor the emergence, spread and intensity of fires.
The important role of the night
The media also presents us with sometimes dramatic images of the desperate operations of the firefighters: they often fail to bring the violent fires under control. However, more attention is often paid to the day – when the fires are raging most intensely. The night, on the other hand, is given less attention, emphasize the researchers led by Jennifer Balch from the University of Colorado in Boulder. According to them, however, this period is of considerable importance. Because at night, the mostly cooler and wetter conditions can slow down fires or sometimes even extinguish them completely. However, a well-known effect of climate change led the researchers to suspect that the importance of the night as a braking factor could dwindle: in recent decades, the nights have warmed up much more intensely than the days.
In order to investigate in more detail how this could affect Balch and her colleagues took an analytical look at the earth from space: Their results are mainly based on evaluations of satellite data on fires in different regions of the world. They not only reflect information about nocturnal fire activity, but also about the conditions that play a role in it. Specifically, it is about the so-called vapor pressure deficit (VPD). This is the difference between the actual humidity of the air and the amount of water it can hold when it is saturated. When the VPD is relatively low, the air is cool and humid – when it is high, the air is hot and dry – more oxidizing conditions are present.
At night it burns more and more
As the researchers report, their data evaluations revealed tens of thousands of fire events around the world: the intensity of nighttime fires increased by 7.2 percent between 2003 and 2020. Regions in both the northern and southern hemispheres of the earth are affected – including Europe. However, the increase was particularly drastic in the western United States, where fires are known to have raged particularly intensely. The scientists report that the fire intensity at night has even increased by 28 percent over the past 20 years.
As part of their study, they have now also shown a VPD limit above which fires can apparently develop particularly well at night. The satellite view of the development of fire-promoting conditions at night revealed that since 1979, one fifth of the world’s fire-prone areas have had an additional week of fire-promoting night-time conditions per year, the scientists report. The west of the USA was again particularly affected – there are eleven more nights a year than before. “Night is the critical time for slowing down an accelerating fire – but the nocturnal brakes on fires are now failing more and more frequently,” says Balch, summing up the significance of the study results.
She and her colleagues fear that this trend will continue: Due to man-made climate change, the night has warmed up much more than the day in recent decades – and this will probably continue. “With the ongoing warming at night, we expect even more fires that will be more intense, larger and spread faster,” says Balch. Finally, she turns her attention to those people who are on the front lines of the problem: “This means that firefighters don’t have the rest breaks they used to have at night – they have to fight the flames around the clock,” according to the scientist.
Source: University of Colorado, professional article: Nature, doi: 10.1038/s41586-021-04325-1