How did climate change affect Los Angeles fires? : NPR

At the beginning of January, the stage was set to a fireplace disaster in Los Angeles. A long, hot summer had dried out the plants and vegetation, which made it more flammable. Drought conditions pulled on as the winter rains had not yet arrived. Then came powerful Santa Ana -Vinde, which won over 80 miles per hour.

The result was more than 16,000 homes and buildings were destroyed after the rapidly moving Eaton and Palisades-Fires exploded. Under these extreme conditions, firefighters had some hope of gaining control of burning.

New studies find fingerprints of climate change in these fires, which made some of the extreme conditions worse. In particular, the warmer temperatures and a drier atmosphere can be linked to heat -catching gases that largely come from burning fossil fuels, according to two different analyzes from the University of California, Los Angeles and World Weather Attribution, a collaboration from international researchers.

Still, for other extreme conditions that led to the fires of Los Angeles, like the strong Santa Ana Ana -Vinde and lack of rain, it is scientifically more difficult.

While there may be a connection to climate change, it is more difficult to recognize considering the very variable weather of the state, which usually swings from wet to dry years. The powerful computer models used by researchers to analyze climate impacts also struggle with very small geographical areas or complex processes, such as the behavior of the fireplace.

Climate scientists develop ways to find out the role that climate change plays in fires. The most significant human influence can still be how the fire started when there were no lightning storms at the time that would have given rise to fires.

“The ignitions were undoubtedly due to human activity,” says Alex Hall, director of the Department of Environment and Sustainability in UCLA. “So basically, I think these fires are man-made. They are man-made. We have to take prevention of ignition much more seriously, especially when we know there will be a very dangerous Santa Ana Wind event.”

Thirsty atmosphere

Los Angeles’ Summer Heating Listed late into the fall of last year, including one Record-breaking September HETE wave. The period from June to December ranked the third hottest since 1895.

A warmer atmosphere is a thirster atmosphere. The dry air pulls moisture out of the plants, making them more susceptible to combustion. Too little vegetation as grass takes drying only hours. For bigger things like trees or even the tree in fences and tires, it can take days or months.

The dryness of Los Angeles’ vegetation before fires was due to both warmer temperatures and lack of rain. An analysis of UCLA found that about a quarter of this moisture deficit was due to the extreme heat affected by climate change.

“The fact that we have a warmer or drier atmosphere today due to global warming will be very likely that large fuels such as dead beams and fence posts and other materials you find in urban environments are drier than they would otherwise be, ”Says Park Williams, a hydrochlimatologist at UCLA. “These fires are very likely more intense and dangerous in urban environments due to global warming.”

Another analysis after world weather attribution found that the hot, dry conditions were approx. 35% more likely due to climate change, measured by Fire wind indexthat looks at temperature, humidity and other weather factors.

Wind and rain

Wind was the biggest factor for the explosive growth of Los Angeles fires and sent showers of glowing into neighborhoods that ignited home.

“The wind speeds were incredibly, incredibly strong, and we had an incredibly dry fuel,” said John Abatzoglou, professor of climatology at the University of California, Merced. “So realistically, this was a perfect storm when it comes to conditions for fire disasters.”

The Santa Ana winds blow when there is an area of ​​high pressure over the southwestern United States pushing air towards southern California and pulling it through the mountains near Los Angeles. Often it warms the air and accelerates the wind speeds, leading to dangerous fire conditions. Researchers are working to understand how the conditions that create these winds could change when the climate is warming but There is still not a clear answer. The conditions may fall or change in the timing.

“Whether climate change affected the wind is very uncertain, very, very complicated,” says Williams.

The impact of climate change on southern California’s rainfall is another challenging question. California saw a wet winter before this one, causing close vegetation to build. The heavy vegetation remained dry this winter under drought conditions.

“Usually we get our first rain, maybe around November, and that’s what kills the fire season, but we didn’t have that rain,” says Hall.

Hall says the precipitating deficit this winter in Los Angeles was a 1-50-year-old event, which means it has a 2% chance of happening in a given year. Whether climate change played a role in that is still unknown. Climate scientists use complex computer models to predict the effects of climate change, but California’s location on the planet makes it difficult to distinguish between what will happen.

“Most of Mexico is expected to dry, and Seattle is expected to generally get wetter and we are right between these two areas,” says Williams. “If our models are off with just a little bit, California could either get drier or wetter. And at the same time, the models are projecting that precipitation will be more extreme in the future, which would make the wet years get wetter and the dry years will be drier.

California’s rainfall is also naturally very variable with huge swings between wet and dry conditions from year to year. It makes it harder to choose a pattern, and the oldest precipitation registrations only go back to the end of the 1800s.

“This means that we need a much longer record to look at things like trends in rainfall to discover the impact of climate change just because the natural oscillations are so big,” Hall says.

Climate scientists are working to refine models of climate change to better simulate fireplace conditions on a smaller scale. It can help areas like Los Angeles to get a better prospect of their future.