Theoretical background on pwsFWI

This page is being worked on but has some issues with references

Introduction

The Fire Weather Index for a personal weather station, in short pwsFWI, is probably one of the most complex modules of CumulusUtils. Not so much for the calculations, which once you know what to do are not that complex, but more for the interpretation and understanding of what is shown. This Wiki article will show the science background to pwsFWI.

For external reference on the theory behind the pwsFWI you can go the The Hot-Dry-Windy Index: A New FireWeather Index site of Michigan State University who adopted it as a tool for climatological analysis. The 2018 article on which I based the software is The Hot-Dry-Windy Index: A New Fire Weather Index. This is an open access article under the Creative Commons Attribution License.

On my (HansR) blog you may read several posts on the pwsFWI but also on the other fire weather indices in the world notably the Canadian FWI. This complex FWI is used in many places but it is so complex that it is not summarized in equations, but referenced by the articles. The complexity of this FWI was one of the main reasons to create pwsFWI. Other fire indexes such as the Ångström index and the Chandler Burning Index, though often seen on amateur weather sites, have been looked at but these are not discriminating enough.

After describing different indices for fire weather, in reverse order. (with longer literature list), At the end of the heatwave, The Ångström index and the FMI index and The Chandler Burning Index, I conclude the following:

Wet wood does not burn easily (if at all); Moisture content of the fuel (wood) is of great importance; Wind does not spark fire but assists drying and is dangerous for propagation; Rain contradicts drying but not immediately; Drying timber in a forest is not a single day event.