Inspired by a post on Nathan Yau’s excellent data visualization blog Flowing Data, showing a calendar view of fatal accidents, I thought I try creating a calendar map with some wildfire data I have been playing with (available from NIFC). This data set includes fire data going back to 1972.
Starting with R calendar map code by Paul Bleicher, I created plots of fires in California for various years.
Looking at the data I noticed a trend of increasing number of fires over the years. To get a better sense of this I tried creating the same type of plot, except aggregating by years and months to get a longer timescale. There is an overall trend showing an increasing number of fires between 1972 and 2007, but this may be due to better reporting. More interesting is what happened in 2007:
- California had more fires in 2007 than in any other year (3245 in 2007 vs. 2569 in 1999, the next highest).
- While fires tend to occur mostly in the summer months, 2007 had more winter fires than other years
I have been digging around in the data to try and figure out if there is anything that can explain this pattern. There are not enough human-caused fires to have a significant effect. Nor does it seem that the El Niño/La Niña weather pattern causes it (See here for a similar plot of El Niño/La Niña patterns). It may have something to do with the Santa Ana winds, but I have yet to find data that could help identify a pattern. Of course, this could also be natural variation and there is no underlying pattern.
I am not a climatologist or an expert on wild fires. The reasons behind this pattern may be obvious to someone who works in these fields. If you have any ideas, let me know.