The Link Between Santa Ana Winds and Wildfires

As we head into the coldest months of the year, a natural phenomenon, known as Santa Ana winds, will start to pick up. These winds are often associated with a few of California's largest and deadliest wildfires.

Santa Ana winds are strong and extremely dry downslope winds, also known as katabatic winds, that affect coastal southern California and northern Baja California. They most often occur during the autumn and winter months between October to March. However, these winds are the most conspicuous between October and January.

There are many different origins to the name “Santa Ana.” The most common and accepted explanation comes from the fact that winds blow through the Santa Ana canyon. Similar weather events occur across the world, most often known as chinook winds in the Rocky Mountains and foehn winds in Norway.

Santa Ana winds form when high pressure builds over the Great Basin, the geographic area bound by the Rocky Mountains to the east and the Sierra Nevada to the west, and low pressure sits over the California coast. The difference in pressure is what makes the wind blow. So, the bigger the difference in pressure, the stronger the winds. The mountain valleys and passes can also enhance wind speeds. Air also blows from high pressure to low pressure, so Santa Ana winds blow east-to-west from the Great Basin to the California coast.

These winds are often hot and very dry. As the air descends downslope from the Great Basin’s high elevation terrain to the low-lying coast, it is forced to warm and compress. By the time the winds hit Los Angeles, the air temperature could have warmed 50 degrees warmer. Warm, compressed air is also very dry. Oftentimes, these winds drop humidity levels to below 20-percent.

Dry, hot winds can be disastrous across southern California. The extreme winds can topple trees and power lines. The dust carried from nearby deserts can wreak havoc on people’s allergies. Most importantly though, these winds are a critical fire weather hazard and fan destructive wildfires.

Researchers from the United States Geological Survey (USGS) examined Santa Ana wind events compared to wildfires. They examined 643 Santa Ana wind events between 1948 and 2018 to learn more about the weather associated with the Santa Ana wind event. The analysis found wind speeds and number of ignitions were strongly and consistently associated with the amount of area burned, while precipitation was a significant factor during some months and time periods. Higher temperatures during or in the months prior to Santa Ana Wind events were generally not associated with the amount of area burned.

Of the 643 Santa Ana wind events, around 25 percent of them had wildfires with 100 percent of the fires being caused by humans, either intentionally or accidentally. Campfires were the leading cause of wildfires from 1948 to 1983, while arson and powerline failures dominated between 1984 and 2018. They also found October is the peak month for Santa Ana wildfires.

 
Source: USGS, Science.org, Wikipedia, UCLA
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Image: Firing Operations on December 21, 2017. (Thomas Fire, Forest Service photo by Stuart Palley)