NWC REU 2021
May 24 - July 30



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Analyzing the Impact of Meteorological Variables on Wildfires in California During the 2020 Fire Season

Theresa Dixon, Helene Peiro, Steven Jester, and Sean Crowell


What is already known:

  • Extremity of wildfires in California have been increasing in the last 5 years, with 2020 being the most intense in its history.
  • The fires are generally classified as flaming or smoldering based on the fire’s heat, smoke content, and ratio of gases released during the burning.
  • Climatology and vegetation of California differs throughout the state and are key factors in the ignition and spread in fires, to account for this a northern and southern region of California was analyzed for this study.
  • Weather conditions like temperature and precipitation are the main variables analyzed when understanding fire weather.

What this study adds:

  • In 2020, positive anomalies in temperature and negative anomalies in precipitation were common for the northern and southern regions.
  • Both regions experienced drought conditions throughout the year which affected the vegetation of the regions and could explain the large fire count for 2020 compared to the 9 previous years. The drought of 2020 could be an impact from the severe La Nina event.
  • The dry conditions in both winter and summer could explain the intense fire of the temperate forest of northern California.
  • Other weather events, such as the Santa Ana wind could impact the fire count and combustion efficiency of the southern region characterized by grassland/savanna vegetation.


In the past 5 years, California has experienced an increase in wildfires during the fire season, resulting from long and dry summers, and in 2020 experienced the most extreme and dangerous wildfires in its history. These 9,917 fires recorded burned over 4 million acres, damaged over 10,000 structures, and caused 33 fatalities. This unprecedented fire event has led to increased interest in fire weather and research on the weather conditions that led to it. Fire weather is described as the meteorological conditions favorable for fire ignition and spread. Additionally, weather conditions have an impact on vegetation fuels and so on fire combustion. The purpose of this study is to focus on 10 years of climatology over northern and southern California characterized by different vegetations to find any trends and anomalies that can explain the extremity of this 2020 event. By using in situ data of temperature and precipitation, we found that 2020 was particularly characterized by an intense drought over the year which could result from a La Niña event. Drought conditions in winter and summer (with positive anomalies of temperature and negative anomalies of precipitation) seem to explain the intense temperate forest fires of the northern region. However, the same conditions in the grassland southern region suggest that other factors might have a role such as the Santa Ana wind. Future studies should hence look at wind and topography information for the grassland southern region.

Full Paper [PDF]