The Regional Meteorology of California Wildfire Emissions

Abstract

Large, damaging, and costly wildfires associated with unusually strong, dry winds have occurred in California recently and through its history. This thesis examines the relationship between daily wildfire emissions and the observed regional meteorology for California’s savanna and forest wildfires over the past 18 years. For each fuel type, the associated weather (daily maximum wind, daily vapor pressure deficient (VPD), and 30-day-prior VPD) is determined for all fire days, the first day of each fire, and the day of maximum emissions of each fire. Emissions for both savanna and forest wildfires are greatly modulated by regional meteorology, with the relationship between emissions and meteorology varying with the amount of emissions, fire location, and fuel type. Weak emissions are generally associated with climatological dryness and winds. For moderate emissions, increasing emissions are associated with higher VPD resulting from temperature increases and only a weak relationship with wind speed. High emissions, which constitute ~85% of the total emissions but only ~4% of the fire days, are associated with strong winds and large VPDs. Examining the meteorology during fires in subregions of California using spatial composites of surface variables, we find that weak-to-moderate emissions are associated with modestly warmer than normal temperatures and light winds across the domain. In contrast, high emissions are associated with strong winds and substantial temperature anomalies, with colder than normal temperatures east of the Sierra Nevada and warmer than normal conditions over the coastal zone and the interior of California.