09 January 2008

Global Wildfire 2007: A sign of climate change?

In the previous post in this series, I discussed wildfire activity observed around the globe in 2007. It was an extremely active fire year , and nearly 100 lives were lost around the world. This post will continue the series, focusing on two related questions: Is wildfire activity increasing? and Is this related to climate change?

There are many telling trends here. Data from the National Interagency Fire Center show generally fewer numbers of fires but more area burnt, particularly since 2000. Many of the events noted in the previous post were unprecedented, including the tundra fires in Alaska, the Greek fires and the California wildfires. The Western US has seen fires of similar magnitude several times over the past few years. The Victorian Alps earlier this year burnt areas which experienced a similarly large wildfire in 2003. These so-called mega-fires are becoming increasingly common, despite the ever-increasing amount of money and resources devoted to wildfire suppression.

Despite these apparent trends, the honest answer to the questions above must be “We don't know”. Large, devastating wildfires have also been seen in the past. The available data records are short and/or sparse; a lot of work remains to be done on cleaning up and filling in gaps in the data. Whatever data there are is also confounded by human activity. Using simple metrics like area burnt or the number of fires can also be misleading, as fire management practices have changed over the years. Our detection and surveillance of fires is much more efficient than in the past, especially in remote regions of the world. Still, there are many reasons to think that they are increasing and that climate change is to blame.

Analogous to the classic Fire Triangle, three interacting factors all have to be present for a wildfire to occur. First, suitable atmospheric conditions, given by the weather and/or climate must be present. Second, adequate fuel amounts and types must be available for combustion. Finally, ignition must occur. If one of these is missing, then a wildfire cannot occur. All of these factors are subject to change with global warming. Indeed, the changes are already being seen.

Most obvious are direct changes in the weather and climate. Temperatures are increasing and droughts are becoming more frequent. Both of these have a direct impact of fire weather. Indeed, research has shown that in SE Australia an upward trend in fire weather has been observed, especially since 2001 or so. Additionally, factors such as the changing of the seasonal timing (e.g. spring starting earlier) are a direct result of global warming affecting atmospheric conditions and hence wildfire.

Changes in fuel conditions are also expected with enhanced CO2 and climate change. Enhanced CO2 acts to fertilize plants, potentially making more fuel available for burning. Further, changes in the types of fuels are likely to result, with shrubs and other woody plants replacing grasslands in many parts of the world as a result of increasing CO2. This could change the frequency and intensity of fire in a given location (even decreasing it...). Invasive weeds and plants can also move, driven by climate change, and alter the fire regime of a place.

Global warming is also driving changes in fuel through other more subtle means. Pine beetles are infesting trees in Canada, killing trees and making them available for burning. The less-intense winter observed in recent years has failed control the population of the beetles, resulting in more widespread infestations. Similar infestations have been reported in the northwestern United States.

Climate change skeptics often claim that the apparent increase in wildfires is solely due to fuel management practices -- not enough prescriptive fire to prevent fuel from building to dangerous levels. But if atmospheric conditions are not conducive to burning, then no wildfire will occur. The weather and climate also act to grow the fuel, prepare it for combustion and spread the flames once started. The recent fires in southern California suggest otherwise; many of the regions burnt this year burnt just 4 years ago.

Lightning is a natural source of ignition for wildfires, especially when it occurs in thunderstorms with low precipitation. It is not known how global warming will affect such storms, but with more widespread drought conditions, it seems reasonable to think that more such storms could be a possibility. Unfortunately, a large fraction of wildfire ignitions are arson related (about 50% in Australia) or have other human causes. But this should not be taken as an excuse or a special category of fires. Humans have always caused fires. For countless generations before European contact in Australia the Aborigines were lighting fires, helping shape the landscape into its current fire-conducive state. The same is true of other indigenous cultures as well. Humans are part of the natural environment and we ignore this at our own peril.

Wildfire activity is predicted to increases as a result of climate change. Indeed, the available evidence suggests that we are already seeing some of that increase, but we cannot answer the question with an unequivocal 'Yes' at this point in time. Nonetheless, society needs to begin considering the possibility and prepare for the effects. Even should the current observed levels of activity not be climate change-driven (unlikely!), the fire activity of recent years provides a good archetype for the types of disasters we can expect. Management strategies will have to be adjusted and considered beforehand. As will be discussed in the next part of the series, wildfires have many more implications than simply 'stuff burning down'. Planning and forethought will be needed to overcome the most deleterious effects.


Image: Canberra Bushfire 2003 from BBC News

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