One Quarter

The CZU Lightning Complex fire is the most significant event to happen to the forest of the Santa Cruz Mountains since the clearcut era.

A while back I attempted to estimate the extent of damage by measuring the area of the fire and the total forested areas of the Santa Cruz Mountains using Google Earth’s handy area measuring tool. I came up with 17% (about 1/6th) of the forest impacted by this fire.

The only problems with my approach are that 1) I used Google Earth’s default satellite view to estimate the forest area based on color and it’s actually kind of difficult to distinguish forests from not-forest by eyeballing it like that. And 2) I used Google Earth’s somewhat crude polygon tool to create an imprecise outline to measure the areas so there was probably some error there.

Today, I decided to make a more serious measurement and so I did a bit of research and found the USGS’s National Land Cover Database. The NLCD uses Landsat satellite imagery to classify land cover. Adding that data layer to Google Earth, I was able to get a much better picture of the boundaries of the forest and even to see the composition of the forest from evergreen to mixed to deciduous.

Then, rather than using Google Earth’s crude measuring tool, I took screenshots from Earth and opened them in Photoshop where I could select color ranges and count pixels (pixel counts are found in the Histogram dialog.) This should be a much more accurate reading.

And here’s what I found. My initial calculation was close, but underestimated the size of the CZU fire damage. My first estimate was about 16% of the forest of the Santa Cruz Mountains in the burn area. With the new, hopefully more accurate approach, that estimate grew to 19% or almost 1/5th.

And with the NLCD data I was able to go a step further and focus in on just the evergreen stands which are primarily made up of coast redwood and Douglas fir. When I analyzed those areas I got an even larger number, 25%. A full quarter of the pure evergreens stands in the Santa Cruz Mountain was impacted by this fire.

Google Earth's satellite view of the Santa Cruz Mountains

NLCD 2016 Land Cover for the Santa Cruz Mountains