This article will focus on the Forest Fire Danger Index (FFDI). You might know it from those big rainbow meters at the entrance to national parks. Being situated well into the Blue Mountains, Blaxland have several of those meters. Another theme of this article are the suggested flight path convergence zones over the Blue Mountains that are suggested in the Environmental impact statement and plans for the future airport at Badgerys Creek. One of them, over Blaxland, is explicitly discussed as an option.

FFDI is calculated using a set of atmospheric conditions such wind speed and temperature, and accumulation of other elements such as precipitation and fire fuel load. Fuel load in and around Blaxland is substantial, a fact that is manifested by the presence of the meters and recurring fires. The other ingredient, precipitation, is yet another focus of this article. The accumulation of precipitation in the years, seasons, months and days preceding the present affects the susceptibility of fires starting and going out of control. Note that, while precipitation that occurs days before the present has a direct effect, a change precipitation in the preceding years and seasons is also crucial. It is known that in the Blue Mountains a fire season that arrives after a year or two with below average rainfall tends to have more and more serious fires. The reason behind this is quite clear - even a small reduction in moisture have a big effect, considering the available fuel load in the Blue Mountains.

Now, the indicative flight path in the draft Environmental Impact statement (EIS) and airport plans suggest a key convergence zone over Blaxland. This flight path is said to be indicative, which places the entire EIS in question. One assumes that this was done to avoid political pressures from those who would be affected. But given that this is all we have to work with, we will assume that there would be a single convergence zone over Blaxland, operating 24/7 with planes passing at 5000-7000 feet and 1-15 minutes apart.

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How is that related to fire danger? The direct effects of planes are heat (300-600 deg. at the output), turbulence and aerosols (i.e. pollution). All of this can affect precipitation and depending on elements such as the type of cloud and other atmospheric conditions can suppress of increase precipitation. Based on the literature (Tao et al. 2011) and given the type of clouds and conditions in the area, our guess is that the general effect would be suppression of rainfall.

One can assume that the day-to-day changes of this effect would be small and perhaps even unobserved changes in rainfall and atmospheric conditions. But we are interested in long term year-by-year local and regional changes and, as we mentioned earlier, even small changes can have serious effects considering the fuel load int eh region.

The good news are that these changes can be verified and measured by simulation. This is something that we are about to test - something that the department of infrastructure and the EIS drafters should have done if they took their work seriously. Nonetheless, these effects can be quantified, and the changes to forest fire patterns can be understood in terms of the Forest Fire Danger Index.

The finding of such a study would be of great interest to affected residents as well as insurance companies. We also note that long term effects of the proposed airport on humans and environment alike are a big hole in the EIS. As one of our experts noted (see here) pollutants such as lead accumulate over time to have substantial health, social and economical effects.

These is yet another example of how "environment" equates to $$$.