Anyone who has ever watched the annual Tournament of Roses Parade on New Year’s Day, the parade that precedes the Rose Bowl, may have seen the (occasionally) snow-capped San Gabriel Mountains towering in the background. Pasadena, California, where the parade takes place, abuts Los Angeles on the northeast, in the foothills at the western end of the San Gabriel range.
East of the San Gabriels rise the taller San Bernardino Mountains, where Los Angeles County, the most populous in the United States, gives way to San Bernardino County, the country’s largest in area. High in the San Bernardino Mountains are the headwaters of the Santa Ana River, whose watershed drains southwest through San Bernardino County, swelling to river-breadth as it veers south through Orange County to empty into the Pacific.
Angelenos have long called the hot winds blowing across the Santa Ann River from the inland deserts the “Santa Anas.” Usually, of course, the prevailing winds are the moistening westerlies rolling in off the Pacific Ocean. But when the direction reverses, Southern California’s coastal counties, already arid, can become desert-dry in a day or two, and the fire hazard can grow extreme.
Until now, the usual Santa Ana wind event has lasted only two or three days. But climate scientists have been warning us that once rare and extreme events like the Santa Ana winds are about to become both more extreme and less rare. 2017—and not in Southern California alone—was a year in which those predictions became frightening actuality. As I write at the turn of the year, the Santa Anas have been blowing on and off since December 4, and there is no guarantee that the current lull will not be followed by another flare-up. When the fires first broke out, Southern California was already exceptionally warm and exceptionally dry. On October 24, Dodger Stadium hosted the hottest World Series game ever held: 103 degrees. November 23 broke the all-time Los Angeles Thanksgiving Day heat record: 92 degrees.
Fire has, of course, been a perennial danger in parched Southern California. But protracted drought—with shortened winters and worsened beetle infestation—has brought about the death-in-place of an estimated 29 million trees on California’s mountains: fuel just waiting for the kindling spark. And when they go, those trees take with them California’s most important carbon sink.