Grass with raindrops on it and text

New Study: Wet Winters No Longer Dampen Wildfire Risk

With the substantial rainfall our region has received in recent months, it’s easy to be lulled into thinking that the wildfire risk for the upcoming fire season has been neutralized.


But let's stay vigilant.


According to a recent study by an international team of scientists, the historic correlation between precipitation in California and wildfire risk weakened over time and eventually disappeared. Between 1600 and 1903, wet winters brought on by the North Pacific Jet stream were typically followed by low wildfire activity, and dry winters were generally followed by higher wildfire activity.


Around the turn of the 20th century (1904 to be precise), the connection between winter moisture and wildfires weakened until it eventually disappeared altogether after 1977.


“Now, fuel buildup from decades of fire suppression in the 20th century plus rising temperatures from climate change means any year may have large fires, no matter how wet the previous winter,” according to a US Geological Survey (USGS) article, citing the findings of the study published in the March 4 issue of the Proceedings of the National Academy of Sciences. 


Large fires, such as the Tubbs Fire and the Thomas Fire, occurred in 2017 after the wet winter season of 2016-2017.


Rainfall to Date in SD Region

The seasonal rainfall for the winter months of December through March was 150%-200% of normal for most of the San Diego-South Orange County region. Our season-to-date rainfall (Oct. 1 through today) is 11.46 inches. In comparison:

  • The normal season-to-date is 8.62 inches.
  • The normal annual rainfall is 10.3 inches.

Parts of the back country (including Julian and Palomar Mountain) have seen over 30 inches of rain. According to the National Weather Service, from October through the end of February, we had measurable rainfall on 31 days. The last time this much rainfall was recorded locally was in the winter of 2016-2017.


Due to the above average rainfall, weeds and grasses are sprouting everywhere and plants are growing. When the weather gets hot, they will dry out, making grass fires more likely. Historically, grass fires tend to occur in the summer, and they tend to be not as destructive as the Santa Ana wind-driven fires that occur in the fall.  But nevertheless dried grass can contribute to the spread of a wind-driven fire.


To Learn More

Read the USGS summary of the study here and the San Diego Union-Tribune’s coverage of the study here.