Looking at Centuries of California’s Climate to Understand Fire Risk

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Wildfire season has, unfortunately, begun to expand its boundaries in many parts of the world. Climate change has amplified certain characteristics of our global weather patterns, creating periods of hotter, drier, colder, and wetter weather in vulnerable areas. Hotter and drier weather has caused wildfire season, once consolidated to a few areas over a few months, to lengthen in duration and extremity.

California has undergone a year of high fire danger. The wildfires that once swept through more rural areas are now threatening suburbs and larger metropolitan areas. As these fires continue to cause damage to people and the environment, scientists are working to assess the many factors that are contributing to wildfire danger in California and beyond.


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Modeling California Climate Data

Contributors to the study included the Centre for Materials and Coastal Research in Germany, the Integrated Climate System Analysis and Prediction at the University of Hamburg, the University of Arizona’s Laboratory of Tree-Ring Research, and the Department of Geography and the Earth and Environmental Systems Institute at Penn State University.

Using climate models and centuries of paleoclimate data (between 1571 to 2013), researchers looked at moisture patterns and atmospheric wind conditions to assess future fire danger in California. The team of scientists from different disciplines worked on paleoclimate data, paleoecology, wildfire research, and other factors that have influenced wildfires across hundreds of years.

Fire Danger and the Jet Stream

Moisture levels in California are highly regulated by the North Pacific Jet stream. The NPJ brings high-altitude winds that bring cooler, wetter air in cooler months, typically December and January. In standard years, the character of the NPJ from year to year can help predict the severity of the fire season when the months become hotter and drier.

The North Pacific Jet (NPJ) travels eastward at variable wind speeds and directions toward California at an altitude of about 11 kilometers above the ocean’s surface. Image: NOAA
The North Pacific Jet (NPJ) travels eastward at variable wind speeds and directions toward California at an altitude of about 11 kilometers above the ocean’s surface. Image: NOAA

The study focused on winter NPJ variability over 400 years. Scientists used tree rings, fire data, and other historical weather data to reconstruct climate patterns to be used to connect the NPJ to fire extremes. In the years before 1904, the research showed that a year of high precipitation levels was never followed by a high fire risk year.

However, beginning in 1904, there was a greater use of fire suppression methods being used. After 1904 and in the more recent years, high precipitation years have been followed by years of high fire extremity.

The study found that global warming has contributed to changes in fire extremity despite periods of high precipitation. These changes can contribute to alterations in the distribution of plant and animal species, the compositions of forests, and ecosystems.

Resources:

National Centers for Environmental Education. A Long View of California’s Climate. 4 March 2019. Retrieved from https://www.ncei.noaa.gov/news/california-fire-study

Wahl, Eugene R., E. Zorita, V. Trouet, and A. H. Taylor. Jet stream dynamics, hydroclimate, and fire in California from 1600 CE to present. Proceedings of the National Academy of Sciences Mar 2019, 201815292; DOI:10.1073/pnas.1815292116

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