Monday, March 20, 2017

Both low RH and high wind speeds dry vegetation and result in higher probability of fires.
a) I have divided the wind speed by RH for each day and constructed a formula to give a "drying index" (black curve). Looking at the graph one can see where there could be a strong cumulative effect (many days one after the other where winspeed/RH is high). Above 0 spells danger for the "Drying Index".
b) I also used the Angstrom Index in another formula and calibrated, etc. Above 0 spells danger for my combined "Dryness Linked Fire Index".
Details:
1) The Angstrom Index (a well known index) is evaluated at midday, so I have used maximum temperatures for the day from the 7 day weather forecast. An RH of 0.5 (50%) and a wind speed of 11 km/hour are regarded by me as average (not safe or dangerous). Since 11/0.5=22, one can subtract 22 from windspeed/RH to centre this index at 0, so windspeed/Rh - 22 is centred at 0 (the intention is that above zero is favourable for fires and below is not).
2) The well known Angstrom Index formula is
Ai=RH/20 + (27-T)/10 and a value for Ai greater than 3 is unfavourable for fires and a value less than 3 is favourable for fires (I have seen slightly different opinions on these figures). Anyhow, these Angstrom index figures are a bit confusing, so I use my own formula (100)(1/Ai) - 33.333 and then from 0 upwards is favourable for fires and a value below 0 is unfavourable.
1) My dryness index is [ (windspeed/RH) - 22 ]/3 (black curve)
2) My combined Dryness Linked Fire Index formula is
100(1/Ai) - 33.333 + [ (windspeed/RH) - 22 ]/3 (red curve).

Saturday, May 29, 2010

Fire Index

FOR GRAPHS OF FIRE DANGER FOR ONE OR TWO SOUTH AFRICAN CITIES SEE MY FACEBOOK PAGE https://www.facebook.com/Fire-Danger-South-Africa-253180405039717/
PREDICTION OF FIRES (THIS IS NOT AN OFFICIAL PREDICTION): South Africa has a model called the Lowveld Fire Danger Index, officially adopted by The South African Government from 2013. However, the USA uses a model that is very good for predicting fires a month or so ahead, similar to the Chandler Burning Index.
Personally, I am using some software on predictions for fires that I wrote, using equations from the Internet and I am seeing if I can predict the AVERAGE danger of fires two weeks ahead - something like a less sophisticated version of the USA method. The Lowveld (SA Government) model takes into account the rain that has fallen recently, how long since it last rained and also wind speed and relative humidity and temperature. The Chandler Burning Index takes into account averages of relative humidity and temperature using longer term weather forecasts (actually a modified model of the Chandler Burning Index). It is said that there is a high correlation between the Chandler Burning Index and the future occurrence of fires. See http://stillwaterweather.com/chandlerburningindex.php
for a description of the Chandler Burning Index.
See http://www.letabafire.co.za/…/National%20Fire%20Danger%20Ra… for the Lowveld Model (SA Government)
In the Cape mountains fires can be caused by falling rocks - see
http://www.daff.gov.za/…/64a7c7f6bea728c942256dff003131a502…
If your land is mainly grassland, then you could use the McArthur Mark 5 Grassland Fire Danger Meter. Please contact me if you need help on this - I am not an expert, but could help you with inputs.
https://reforestation.me/fire-no-fines-concrete/ has ideas on how to protect people and livestock against fires.

Having a look at some fire danger indexes (also called indices), I did not see any that included direct radiation from the sun, although there might be some. Now we know that if a plant is in the sun its surface temperature gets much hotter than it it is in the shade, so I want to propose another index related to the number of kWh radiation the land receives from the sun in a day. If you look at the evaporation equation at 
http://www.engineeringtoolbox.com/evaporation-water-surface-d_690.html
you will see that evaporation rate depends of the temperature of the water surface and I say the evaporation rate from a plant must depend on the temperature of the surface of the plant. I have written my own software that tells me how many kWh a day is experienced at any specific latitude when the sun is shining. It takes into consideration the air mass the sun shines through at different latitudes and calculates the solar elevation angle for each minute of the day and does an integration, so it is easy for me to calculate values.

FIRE SAFETY - see 
http://www.courts.act.gov.au/__data/assets/pdf_file/0011/977978/submissions_on_behalf_of_mr_p_lucas-smith_and_mr_m_castleattachment1.pdf 

Fire danger calculator

Fire danger calculator at http://zfpa.co.za/fdi.html  (see online calculator).