Human-induced climate change worsened Los Angeles wildfires, says study

Firefighters work as the Hughes Fire burns in Castaic Lake, California, U.S. January 22, 2025. (Photo: Reuters)

“Climate change increased the risk of the devastating LA wildfires. Drought conditions are more frequently pushing into winter, increasing the chance that a fire will break out during the strong Santa Ana winds that can turn small infernos into deadly infernos. Without a faster transition away from planet-heating fossil fuels, California will continue to get hotter, drier and more flammable,” said Clair Barnes, World Weather Attribution researcher at the Centre for Environmental Policy at Imperial College London.

In coastal southern California, which has a Mediterranean climate, with chaparral shrubland that has evolved to survive and recover from fires, grasses and oak trees, wildfires are a natural part of the ecosystem and occur throughout the year. They are usually the largest between July and September due to low fuel moisture caused by a lack of precipitation in summer, high temperatures and low humidity. The arrival of rain between October and December historically marked the end of the wildfire season. The Santa Ana winds typically occur in the cooler months between October and March.

Dry season longer now

The researchers have found that the length of the dry season has increased by about 23 days since pre-industrial times, when Earth was 1.3°C cooler. “This means that, due to the burning of fossil fuels, the dry season, when a lot of fuel is available, and the Santa Ana winds, which are crucial for the initial spread of wildfires, are increasingly overlapping,” says the study. It adds that, in recent decades, the rains have also decreased. Today, low rainfall across the three months is about 2.4 times more likely in neutral El Niño conditions, and a further 1.8 times more likely in La Niña conditions compared to the pre-industrial climate, says the study.

Firefighter Joshua Cari sprays water while battling the Lilac Fire near the Bonsall community of San Diego County, Calif., on Tuesday, Jan. 21, 2025. (AP Photo/Noah Berger)

Hotter air temperatures are also evaporating more moisture from plants, making them easier to burn. Drier, flammable conditions persisting later in the year increase the chance a wildfire will break out during the peak of the Santa Ana winds in December and January, the scientists said.

To determine if climate change has helped promote the low October-December rainfall, lengthened the fire season and fire-prone weather, the scientists combined weather data with climate models.

“However, the models did not perform well, in part due to the small, mountainous study area and the scattered, sparse rainfall. While the models indicated a climate change influence on the hot, dry, and windy conditions, they did not show a significant impact on rainfall or the fire season’s end date. Despite this, the scientists are confident that climate change is an important driver of the changes, based on existing scientific studies and the real-world weather data analysed, which show an increased likelihood of LA fires,” says an official statement from the study.

Firefighter Joshua Cari sprays water while battling the Lilac Fire near the Bonsall community of San Diego County, Calif., on Tuesday, Jan. 21, 2025. (AP Photo/Noah Berger)

Roop Singh, Head of Urban and Attribution at the Red Cross Red Crescent Climate Centre, said, “A deadly combination of factors came together to turn this wildfire into a disaster. Climate change set the stage, helping turn the hills around LA tinder-dry. However, hurricane-force Santa Ana winds, the rapid spread of fires into urban zones, and a strained water system all made the blazes extremely difficult to contain. These fires have highlighted just how vulnerable California is to winter wildfires, underscoring the need for better preparation for a more dangerous future.”