While reading news of the wildfires in Maui, I see that they’re estimating fires are something like 50% or 80% contained. How do they go about calculating that percentage for such a wide area and with the expectation that the fire will continue to grow?
Source: https://www.cnn.com/2023/08/12/us/maui-wildfires-hurricane-dora-saturday/index.html
In: 7
It’s talking about the fire’s borders. You go around the outside border edge of the whole fire and say what % of that border is currently stopped from any further spread (by a manmade firebreak or natural feature like a lake) vs. what % is currently open and free to spread and get bigger.
The **containment % is what % of the fire’s** ***perimeter*** **has been contained**. A wildfire with 25% containment means control lines have been completed around 25% of the fire’s perimeter.
A visual example makes it easy. [Here’s a partially contained fire’s borders](https://media.npr.org/assets/img/2017/12/20/2016_10_23-10.05.46.999-cdt-d4ad27ace0faa13829acf042bd37fdadec598cf7-s800-c85.webp). The border that’s in black is contained by “completed fire breaks”. The border that’s in red is “uncontrolled fire edge”. **The containment % is just what fraction of the total border length is currently red (uncontained).**
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