Santa Ana Winds and Their Impacts on Soutehrn California

Santa Ana winds (SAW) are dry, warm downslope winds that blow episodically from the Great Basin into coastal Southern California. Santa Ana season usually begins in September and ends in May, with most frequent winds in winter, particularly in December, but causing the greatest wildfire hazard in autumn. Southern California has a Mediterranean climate with predominantly wintertime precipitation and hot dry summers. SAWs require a cold dense air mass over the elevated Great Basin. In fall, the Great Basin is cooler than southern California area but not yet very cold -- so the Santa Ana winds can start at a higher temperature and thus reach sea level very hot and extremely dry after compression warming.[1] That hot dry wind blowing after a hot dry summer, produces an especially high fire hazard. SAW-driven wildfires have long lasting and wide-ranging socio-economic and environmental impacts on Southern California, as evidenced by the catastrophic wildfire seasons of 2003 and 2007. The goal of this research is to analyze relationships between Santa Ana winds and wildfires in Southern California, as well as the effects of these wildfires on the community and environment.

A SAW index was used to identify events, describe their climatology, their seasonal and interannual variability, as well as meteorological parameters (wind speed and humidity) that contribute to SAW impacts. These factors were then analyzed with wildfire data and records from the California Department of Forestry and Fire Protection, paying particular attention to the 2003 and 2007 seasons.

Although SAWs influence the intensity, footprint and longevity of wildfires, they do not, in most cases, cause the fires. There is no seasonal cycle in SAW wind speeds, although there is a strong seasonal cycle in SAW frequency and humidity, which suggests that other factors, such as precipitation, vegetation and human interaction, potentially play a role in wildfire frequency, timing and intensity as well, as shown by the investigation into areas of greatest wildfire impacts (fatalities, acres burned, structures burned, and economic loss). We study these relationships in order to inform effective mitigation and/or evacuation strategies as well as to contribute to educational efforts on wildfires and Santa Ana winds that can help save resources and lives.