Fire, fire Climate change exacerbated fires in Southern California according to report

SDA

28.1.2025 - 23:21

Simulations helped the research group to understand the effects of climate change on the extent of the fires. (archive image)
Simulations helped the research group to understand the effects of climate change on the extent of the fires. (archive image)
Keystone

The climate crisis has exacerbated the large fires in Southern California. Dry winds and a lack of rainfall created ideal conditions for the devastating fires, according to a rapid international analysis by a 32-member research group.

Keystone-SDA

Earlier this year, several large fires raged in the Los Angeles area. These fires have so far claimed 29 lives and destroyed over 16,000 buildings. An international research group has now found that man-made climate change has contributed to the intensity and likelihood of these major fires.

Dry winds from the mountains

Forest fires are not uncommon in Southern California. They usually occur from July to September, when humidity is low, temperatures are high and rainfall is low. However, some of the most destructive fires have occurred in the fall and early winter when the Santa Ana winds kick in. These dry winds flow from the inland mountains to the coast.

Although it usually rains more in California from October to December, there was no rainfall during this period. The region has not experienced any significant rainfall since May 2024, as the rapid analysis by the World Weather Attribution (WWA) research initiative at Imperial College London also shows.

Vulnerability of a region

The research group used the "Fire Weather Index" (FWI), which uses meteorological information such as temperature and wind speed to characterize the weather conditions that can influence the size of forest fires. They also examined drought conditions in the months leading up to the fires and compared them with similar patterns from the last seven decades. Simulations helped to understand the effects of climate change on the extent of the fires. The research group came to the following conclusions:

The conditions that determine the "Fire Weather Index" had become more extreme. In today's climate, with global warming of 1.3 degrees Celsius compared to pre-industrial times, these conditions are 35 percent more likely and 6 percent more intense for such large fires. This trend has accelerated in recent decades.

If warming reaches 2.6 degrees Celsius, which is expected by 2100, these fire-promoting conditions will become a further 35 percent more likely.

The lack of precipitation from October to December 2024 would have dried out the vegetation, which would then act as fuel. With current global warming, similar dry seasons occur every 20 years, according to the analysis, making them 2.4 times more likely than in a pre-industrial climate.

The dry season in southern California has been extended by 23 days due to climate change. As a result, the time in which dry plant material is available as fuel overlaps with the Santa Ana wind season. After two very wet winters in 2022/23 and 2023/24, there was plenty of dried-out plant material available, as the precipitation during these winters promoted the growth of grass and shrubs.

Call for better prevention

Based on its analysis, the research team called for improved water infrastructure, stricter building regulations and strategic investment in disaster risk reduction and the expansion of renewable energy.

Roop Singh from the Red Cross Climate Center concluded: "A deadly combination of factors came together to turn this forest fire into a disaster." Climate change had prepared the ground and contributed to the fact that the hills around Los Angeles had become dust-dry. "But hurricane-force Santa Ana winds, the rapid spread of the fires into urban areas and an overburdened water system made containing the fires extremely difficult," Singh said in a statement accompanying the analysis.

"Climate change exacerbates 'fire weather' worldwide"

The research group emphasizes that although the individual results are subject to uncertainties, they all point in the same direction: Climate change has increased the likelihood of fires.

"Attribution studies are a valuable tool for assessing how climate change affects the probability or intensity of conditions that favor forest fires," commented Yoshi Maezumi from the Max Planck Institute for Geoanthropology in Jena. These include, for example, prolonged drought, extreme heat and low humidity.

"However, individual fire events - such as the one in Southern California - cannot be fully attributed to climate change, as ignition sources - often humans - and local factors such as topography play a decisive role," added the researcher. "Nonetheless, there is clear evidence that climate change has exacerbated 'fire weather' globally, with longer fire seasons and more extreme conditions becoming more common in many regions."