PwsFWI

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 try to explain both how the module works, what you get and the value of it.

This page is about the module from a practical point of view, you go to Theoretical background on 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.

The userinterface has two formats: standard and beteljuice which, you guessed it, has been created by beteljuice.

Operation

This module is included in the website. When needed as a single output the following command is given:

  utils/bin/cumulusutils.exe pwsFWI

Output

The output consist of two or three files files:

pwsFWIcurrent.txt
pwsFWI.txt
pwsFWIanalyse.csv (optional, created if the inifile parameter Analyse is greater then 30)

pwsFWIcurrent.txt

This is the file of which the contents is shown on the left side of the menu bar when the website generator is used. User using pwsFWI as a stand-alone can choose how and where to use the contents of this file. It shows the current value of the Fire Weather Index as calculated at the most recent rollover.

pwsFWI.txt

This is the main output of the module containing both the calculations of the past days but also the prediction on the basis of the values of Yourweather.co.uk (see Forecast). It also shows the legend for the colour coded values.

NOTE: The values bear no relation to other fire weather indices (there exist others) but the colour coding does. The colour codes are not formally standardised but informally it comes close to standardisation.

pwsFWIanalyse.csv

Is a comma separated values file with the calculations of the number of days as set in the Inifile parameter Analyse. That number could take up all days in your dataset but be reasonable. It creates the possibility to make your own calculations and checks. This was an important tool during the calibration phase of pwsFWI.

Inifile parameters

   [pwsFWI]
   Analyse=90                                 (number of day written to the analysis file when > 30)
                                              (if number of days is 30 or less no analysis is done)
   WarningLevel=5 | 6                         (highest warning  level is Extreme or Catastrophic)
   ResultFormat=standard | beteljuice         (the format of the output)
   FireImage=true | false                     (flames are shown at the end of the scale)
   predictionURL=[your API string]            (If this string is empty, no prediction is done, see Forecast)
                                              (Choose the XML API, address 2: “Address 2: XML file with the 5-day forecast and detailed information in 3-hour intervals”)
   PredictionBackground=Moccasin              (background colour of the prediction lines)
   CurrentIndexFormat=Standard | Betel-Kocher (the format of the Current value)
   CurrentPwsFWI=                             (this is not a setting but an operational content used by the software)
   CurrentIndexDay=yesterday | today          (the day for which the Current Value is  shown)

Inner working

The software is simply running through the daylist from the day where the user chooses to start: minimal 30 or higher if analysis is on. For each day an entry in the pwsFWI list is created and the following values are calculated (see An effort for a simpler fire weather index):

The saturation pressure of the water vapour (P_sat) using the August Roch equation
The Vapor Pressure Deficit (VPD)
The dayvalue for the pwsFWI by taking the product of the VPD and the windspeed.
This pwdFWI can fluctuate pretty strong between days so some smoothing is done when averaging the pwsFWI value and take the rain days over the previous five days into account which dampens the fluctuations up and down.

The result is the pwsFWI value for that specific day. With prediction on this can be done up to five days into the future. The output is then generated with the calculated list.

The value which is used for the user to display - the Current value - can be set to be today or yesterday (default) according to the value of the inifile parameter CurrentIndexDay. Yesterday is the default because that is the last complete day and thus (true) day. Today is still to be measured and therefore is a prediction.

For the output the chosen format is used with a warning level 5 or 6 depending on the choice of the user. 5 means a maximum warning level of Extreme fire danger and 6 means a maximum warning level of Catastrophic. Catastrophic has been added as a warning level in Australia some years ago. The warning levels have been calibrated (non-scientifically) during the first year and were correct according to other systems.