Apr 11, 2012

How to predict a wildfire?

Wildfires are impossible to predict,

Or are they?

The above chart uses water level data collected at the L28Gap hydrologic monitoring station to show levels of drought severity.  Small/cool data points indicated low fire severity and warm/large data points indicate increasing drought severity.  The summer sheetflow season is denoted with the small blue dots, on top of which are labeled major meteorologic events of note, i.e. Mitch, Fay, Wilma.  Green data points indicate period when natural fire breaks are still fully flooded.  Yellow data points indicate periods when natural fire breaks are starting to dwindle.  Orange and red denote periods when standing water is absent.  Synthesis:  You can never predict a wildfire, but it's easy to see that major wildfires tend to strike in late spring when the water table has dropped down into extreme drought and lightning activity increases.


The graph above plots drought severity relative to water table depth at a station located in the middle of Big Cypress National Preserve called L28Gap from 1980 to present.  The name of this station has always been a point of confusion because the physiographic L28 Gap actually lies quite a far distance away -- 15 miles to the southeast -- in a levee-less and canal free "gap" in the otherwise semi-contiguous L-28 earthen berm that forms the western boundary of Water Conservation Area 3 (WCA3).  The name of the station is hydrologic, not physiographic: it was installed by the South Florida Water Management District (SFWMD) to measure the rate and duration of discharge flowing through the "7.5 mile gap" between the downstream terminus of the L-28 Interceptor and the L-28 Tieback to the south.  The gap was left in the levee to allow water to free-flow out of the Big Cypress into the Everglades instead of having to pump it over a levee.

But that's a side story.


My point is that we just don't measure water just to measure water, but also (as is the case in the graph above) to look at its absence better and more commonly known as drought. However, water isn't just present or absent, like a flip of a switch. Nor do instances of extreme drought develop over night.

April and May, combined with increased lightning strikes, is when major wildfires occur most.

The shadow means the tree in the foreground didn't die.
(Wait a minute, I think that only applies with vampires!)

This year's drought isn't so bad ... yet.

Compare that to the last year when, for four months, extreme drought prevailed.  Towards the end of that period is when the wildfire called Jarhead struck.  Fire can run free across the swamp when all the natural shallow water breaks have run dry.  Historically you can see similar large fires also coincide with deep dips of the water table into the drought-stricken red zone.


For example, Turner Ten (1981) jumps out very clearly on the chart.

Also, absence of major wildfires during the generally wetter 1990s is easy to see.

The marsh on the left was still holding water,
thus explaining why it didn't burn.

To be sure, you can never predict a wildfire ...

But they sure make sense in retrospect as plotted on the historic water chart.

3 comments:

Rick said...

Mention of 1981's Turner River fire brings back memories. I was working for FL DOF (now Florida Forest Service) at the "Miles City" fire tower at the time. Miles City is where the Florida Panther Bunkhouse is now. Everyone knew conditions were extremely dry.Everyone except the Park Supt, Chief Ranger and Chief of Resources for the recently established Preserve. They were all new to the area and based on their decisions early in this fire event, they did not understand the concepts Bob has pointed out. While I admit to having the the luxury of hindsite, early and assertive intial attack on the Turner 10 may have changed the narritive considerably

Robert Sobczak said...

Thanks for your comment, Rick. It's interesting to hear your perspective.

Janie said...

Dry conditions certainly make wildfires more likely. With minimal precipitation in the west this year, we'll probably see more than usual wildfire activity.