Wind

Wind affects wildfire behavior primarily by helping to spread a fire once it has started; wind also promotes drying through enhanced evapotranspiration. Strong downsloping winds across mountain ranges are significant factors in wildfire spread. These winds – called Santa Ana winds, Chinooks, foehn winds, and Diablos, depending on their location – can sometimes reach hurricane force.

In California, Santa Ana and Diablo winds occur when a large high-pressure ridge situated just east of the Sierras and the related clockwise airflow cause downsloping easterly winds. Low pressure off the California Coast can enhance this easterly flow. Winds get channeled through narrow mountain passes, enhancing their speeds. Driven by this large-scale pattern, air that is repeatedly lifted before descending further will become warm and dry, potentially drying vegetation and spreading fires.

A study by Guzman-Morales and Gershunov (2019) found that Santa Ana winds have decreased in intensity and frequency over the last several decades. Their analysis of model output from GCMs also suggested that the decreased trend will continue into the future. Gershunov et al. (2021), however, found that distinct dynamics form relatively hot or cold Santa Ana Winds, and that climate change may increase the hot variety, thus causing more catastrophic wildfires, especially during anomalously dry winters.