2021 Study: ‘All [Santa Ana] fires are the result of human ignitions’
Autumn and winter Santa Ana wind (SAW)–driven wildfires play a substantial role in area burned and societal losses in southern California.
Temperature during the event and antecedent precipitation in the week or month prior play a minor role in determining area burned. Burning is dependent on wind intensity and number of human-ignited fires. Over 75% of all SAW events generate no fires; rather, fires during a SAW event are dependent on a fire being ignited.
Models explained 40 to 50% of area burned, with number of ignitions being the strongest variable. One hundred percent of SAW fires were human caused, and in the past decade, powerline failures have been the dominant cause.
Future fire losses can be reduced by greater emphasis on maintenance of utility lines and attention to planning urban growth in ways that reduce the potential for powerline ignitions.
In summary, SAW (Santa Ana wind) speed is an important factor determining area burned, but SAW events by themselves do not predict large fire events; over 75% of all wind events result in no fires.
Even extreme winds do not always result in large fires, e.g., events with two and three extreme SAW days had little or no area burned. Thus, a major limiting factor to large fires is whether or not there is an ignition that escapes initial attack during the wind event, and the probability of this increases with the number of fires ignited.
The importance of this factor cannot be underestimated, as in all months the effect of number of ignitions during a wind event is a major factor determining area burned. In the southern California region, 100% of all SAW fires are the result of human ignitions, either intentionally or accidentally.
Over the past 71 years, the sources have changed markedly, with arson, and especially powerline failures, becoming more frequent in the latter part of the 20th century (27, 28). This pattern is evident in other regions subjected to autumn wind-driven fires such as the North Bay counties in the state, where powerlines have become a major source of fires.
Two factors account for this: a history of inadequate maintenance of powerlines and increased expansion of the power grid (4). The former potential cause is being addressed by utility companies; however, the role of how to manage population growth in ways that would minimize expansion of distribution/transmission lines vulnerable to SAW winds has received little or no attention.
…Fires >1000 ha burned were not associated with higher temperatures (Fig. 2DOpens in image viewer).
Even for very large SAW (Santa Ana wind) fires (>5000 ha), the Tmax during these SAW events was not significantly higher than the average for a SAW event that month (P = 0.705 to 0.853 for October, December, and January with one-sample t test); in fact, Tmax in November during events with >5000 ha burned was significantly lower than the long-term November mean (P = 0.004, n = 11).
Precipitation in the week before SAWs event likewise did not appear to play a substantial role (Fig. 2EOpens in image viewer).
“In the southern California region, 100% of all SAW [Santa Ana] fires are the result of human ignitions, either intentionally or accidentally. Over the past 71 years, the sources have changed markedly, with arson, and especially powerline failures, becoming more frequent in the… pic.twitter.com/qRm6qe8U0z
— The Honest Broker (@RogerPielkeJr) January 8, 2025
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bill
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Oh pulleze chicken little.
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