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08 September 2011

Texas Burns But What's the Global Fire Trend?


Wildfires that have destroyed more than a thousand homes and threaten thousands more continue to rage in central Texas. Meteorologists point out that drought and an influx of wind from Tropical Storm Lee have fanned the flames and fueled the rash of fires, the most severe Texas has experienced in recent memory.

But what do we know about the broader context of the fires? Can we say with any certainty, for example, that fires have become more common in the United States – and across the globe – in the last few decades as global temperatures have increased?

The answer to that question, I found after hunting through the various journal articles and checking in with some of Goddard Space Flight Center's fire specialists, is complex. Satellites offer the most comprehensive and reliable measure of the amount of land burned each year; however, satellite-based records of fire activity are still relatively brief.

The longest fire record I’ve seen published so far, a piece of research authored by Goddard's Louis Giglio and the University of California, Irvine’s James Randerson, goes back about thirteen years, not long enough to make particularly definitive statements about the nature of long term trends.

Still, Giglio and his colleagues have pieced together hints of trends that are worth noting. Between 1997 and 2008, they show that the number of hectares burned across the globe has declined a significant amount from a maximum in 1998 to a minimum in 2008 (see graph above). The area burned in the United States, which is less than a percent of the total area burned each year, has seen peaks in 2000 and 2007 (see graph below).


What’s driving the global decline in area burned? The topic is ripe for more research, but when I asked Giglio that question he reminded me that, contrary to what one might expect, increasing global temperatures and drought do not invariably produce increases in fire activity.

The local vegetation and climate makes a big difference, Giglio explained, noting that in certain water-limited areas, such as portions of Australia and Africa, drought can actually make wildfires less likely to occur by limiting the growth of fuel. (The opposite, however, is true in places that receive moderate amounts of rain during the wet season, such as the western United States, a region for which its thought that drought will increases fire activity.)

For more on this topic, read Giglio and Randerson’s study in the journal Biogeosciences. For more on how satellite are used to monitor wildfires, visit the University of Maryland’s MODIS fire monitoring page. For a NOAA website that highlights fire trend data, visit this page.

Text and graphics by Adam Voiland. Graphics based on satellite-derived burned area data published by Louis Giglio in 2010 (see table 2).

- NASA BLOG