With the start yesterday of the Cabin Fire in the Angeles National Forest, and the requisite fear that it will become another Station Fire, I decided to take a quick look at the history of wildfires in Southern California. The California Department of Forestry and Fire Protection’s Fire and Resource Assessment Program (FRAP) generates a lot of geospatial data that it disseminates for free to the general public. One of these is a layer containing the boundaries of all known fires 10 acres or greater since 1878. That data set is provided as an ESRI File Geodatabase and is shown below.

Boundaries of historical fires in California from 1878 to 2014.
Boundaries of historical fires in California from 1878 to 2014.

Using QGIS 2.10, I selected fires in southern California, roughly defined as Point Concepcion south to the border with Mexico.

Selecting southern California fire perimeters.
Selecting southern California fire perimeters.

I then export the data to an ESRI Shapefile.

Southern California fire perimeters.
Southern California fire perimeters.

From here on out, I’ll leave the GIS world and manipulate the data table from the southern California layer in Excel. The image below shows the data fields in the shapefile’s DBF table. I’ll save the DBF as an Excel file.

Data fields from the fire data as viewed in Excel.
Data fields from the fire data as viewed in Excel.

I then need to convert the ALARM_DATE (date fire started) and CONT_DATE (fire containment date) to date formats that are usable in Excel. I create fields next to them, and modify the date fields using the formula:

=DATE(LEFT(A1,4),MID(A1,5,2),RIGHT(A1,2))

Throwing out the handful of rows with bad date values, the result shows that there have been approximately 6,329 wildfires in southern California since 1902.

I first want to look at how many acres have burned per year. To do that, I create a pivot table, using the Year column and then the sum of the GIS_ACRES field. I then create a chart based on that table. I include a trend line on the chart, which seems to indicate a definite increase in fire frequency.

fires5
Total acreage of southern California fires each year. The trend line (dashed) seems to indicate an increase since 1902.

How about looking at the acreage burned per month?

Historical acreage burned per month in southern California.
Historical acreage burned per month in southern California.

If I only include data since January 1, 2000, it looks a little different:

Monthly acreage of fires in southern California since 2000.
Monthly acreage of fires in southern California since 2000.

There have been 447 fires in the Angeles National Forest between 1910 and 2014.

Historical fires in the Angeles National Forest in terms of acreage per month.
Historical fires in the Angeles National Forest in terms of acreage per month.

The obvious peak in August is clearly because of the 2009 Station Fire. The total historical burn acreage for the ANF from all fires is 655,602 acres. The Station Fire was 160,833 acres. Removing the Station Fire from the data paints a very different picture and shows a fairly steady fire risk through the middle and late summer and early fall.

Historical ANF fire data with the Station Fire removed.
Historical ANF fire data with the Station Fire removed.

I may play around with the data some more when I get the time.

2 thoughts on “A Quick and Dirty Look at Historical Fires in Southern California

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