A Drier, Hotter Future?

Drought and Wildfires in California

California's ongoing drought is worsening, with Governor Brown declaring a state of emergency in January 2014 and this year's snowfall at historic lows. One risk of drought is that it will increase the danger of damaging wildfires.

We provide initial findings and a platform for exploration and analysis of the historic relationship between drought and wildfire in California. This allows stakeholders to better understand how continued drought may increase the risk for catastrophic wildfires.

California Wildfire History

While 2013's Yosemite Rim Fire was the most recent to receive national media coverage, Californians know the long history of damaging wildfires across the state. Driven by a string of major fire seasons from 2006-2008, California has seen increasing numbers of acres burned across the state over the past twenty years, and it is expected that the number of acres burned annually by wildfires may increase to as much as 310% of current burn by 2050.

Wildfires cause loss of human life, extensive damage to private property, and can have long-term health consequences for communities and ecosystems affected by wildfires. With California also accounting for the highest per-acre cost for large wildfire suppression, budget concerns are becoming increasingly urgent.

California Drought History

Measuring Drought

Drought is typically associated with a lack of rain, but it’s a little more complicated than that. “Normal” precipitation differs among regions of the United States, so the country is divided into 344 regions for climate monitoring.

The Palmer Drought Severity Index (PDSI) was developed for comparing drought conditions between different regions. PDSI is based on precipitation, with positive values indicating wet spells and negative values indicating dry spells.

The charts below show annual precipitation and PDSI averaged over the entire state for the period of 1993 through 2011. California’s rainy season extends from November to March, during which time the state typically receives 75% of its annual precipitation. Notice in the charts below how years with low rainfall coincide with droughts and negative PDSI.

Palmer Drought Severity Index

Condition PDSI Range
Extreme wet spell Greater than 4.0
Severe wet spell 3.0 to 3.9
Mild to Moderate wet spell 1.0 to 2.9
Near Normal -0.9 to 0.9
Mild to Moderate drought -2.9 to -1.0
Severe drought -3.9 to -3.0
Extreme drought Less than -4.0

Regional Patterns

These grid maps show how average precipitation and PDSI change year to year. Use the toolbar on the right to move through the years and see how precipitation levels affect drought differently across the state's climate regions.

Wildfire and Drought:

Patterns and Relationships

Applying the same grid pattern to wildfires yielded number of acres burned during drought and non-drought periods for each node. While wildfires are distributed differently across the distinct climate divisions of California, both Northern and Southern California showed significant overall increases in acres burned during drought periods.

The chart below shows ratio of acres burned in drought periods to acres burned in non-drought periods. More acres were burned during drought periods in every region except the Central Coast and San Joaquin.

Investigating just the California wildfire season, June through October, helps clarify the relationship between drought and fire. All major fires and fire seasons since August 1996 have occured during drought years. Importantly, it is clear that the relationship between drought and wildfire is particularly driven by a set of five to ten months over the past decade with particularly large fires. Future investigation into these specific fires could be valuable for developing fire management strategies that will be particularly effective during droughts.


The relationship between drought and wildfire in California is incredibly complex, and relates to diverse inputs ranging across climate change, irrigation patterns, wildfire management strategies and even individual cases of arson. However, our analysis suggests a significant pattern of increasing drought and increasing acres burned by wildfires across much of the state.

Neither drought nor wildfire are problems that will be resolved in the near term. As Californians continue to combat and adapt to their changing environment, there are no easy answers. However, a better understanding of how natural disasters like drought and wildfire interact can help citizens, administrators and politicans understand the hard choices that need to be made in how best to manage these challenges.


This website was created by Cameron Reed, Peter Swigert, and Xavier Malina as the final project for Information Visualization, a course at the UC Berkeley School of Information.

The visualizations were created with Tableau and are based on the US Forest Service wildfire database, originally accessed through the National Park Service, and historical drought datasets accessed the National Climatic Data Center. The website was designed using Cool Kitten, a framework by Jalxob.

Additional drought information sources: El Niño years, PDSI Explanation, and California Drought.

See project code on GitHub.