NASA Takes A Look Back At A Decade Of Fires

NASA Takes A Look Back At A Decade Of Fires

20 October 2011



For more than a decade, instruments on Terra and Aqua, two of NASAs flagship Earth-observing satellites, have scanned the surface of our planet for fires four times a day. The instruments, both Moderate Resolution Imaging Spectroradiometers (MODIS), have revolutionized what scientists know about fires role in land cover change, ecosystem processes, and the global carbon cycle by allowing researchers to map the characteristics and global distribution of fires in remarkable detail.

The two instruments have detected more than 40 million actively burning fires and observed nearly 10 billion acres of charred land during tens of thousands of orbits. They have extended and refined upon about 20 years of data from a predecessor instrument  the Advanced Very High Resolution Radiometer (AVHRR)  that orbited aboard a series of polar-orbiting weather satellites managed by the National Oceanic and Atmospheric Administration (NOAA).

The unique and comprehensive view of fire that MODIS offers is distinct from anything that aircraft or field research can provide. MODIS data have enabled a tremendous amount of new fire research, and there will be more to come as the records extend into the future, said Chris Justice, a University of Maryland scientist who has led the effort to use the MODIS instruments to monitor fires. Its essential that we maintain the long-term records of active fire and burned area that MODIS has established and continue them with NPP VIIRS if we want to understand where and how fires are responding to climate change and the activities of a growing human population, he said.


Mapping: The Geography of Fire


That all began to change in 1980 when University of California, Santa Barbara scientist Jeff Dozier and NOAA scientist Michael Matson first noticed a series of tiny white specks on an image of the Persian Gulf captured by an AVHRR instrument on a NOAA satellite. Those specks turned out to be the thermal signature of gas flares from oil fields, said Dozier. The gas flares were the first actively burning fires detected from space, and the mathematical method Dozier devised to detect them serves as the foundation of the method still used today.


However, AVHRR had not been designed for fire monitoring and had a number of weaknesses. It couldnt, for example, pinpoint fires particularly well; it missed many fires in regions with hot or highly reflective backgrounds; and it couldnt distinguish between smoldering and vigorously burning fires.


Over that period, striking patterns have emerged from the MODIS data. Its not an exaggeration to call Earth the fire planet, said Justice. On an average day in August, MODIS typically detects some 10,000 actively burning fires around the world. A full 30 percent of the land surface is affected by fire. And during any given year, MODIS has shown, about three percent of the worlds land surface has clear burn scars visible to the satellites.

One of the most noticeable patterns to emerge is the sheer abundance of burning that occurs in Africa. MODIS has demonstrated that some 70 percent of the worlds fires occur in Africa, and more than 50 percent of the total area burned in the last two decades has occurred on that continent, due largely to the extensive burning of savanna grasslands during the dry season.

MODIS imagery also highlights that other parts of the world  such as southeastern Asia, the Indo-Gangetic Plain, eastern Europe, and the tropical forests of Indonesia and Amazonia  experience regular burning seasons linked to agricultural practices, but in none of these areas does the scope of the burning rival what occurs in the African savannas.

The high-quality and continuous nature of MODIS records has allowed scientists to begin searching for long-term trends. Ten years of data arent long enough to say were seeing a real trend, but MODIS has given us some interesting hints about the direction we seem to be headed, said Louis Giglio, a University of Maryland scientist who has played a leading role in advancing the scientific algorithms used to detect fires and in processing MODIS fire data.

Overall, the satellites show that the area burned across the globe has declined by about ten percent over the last 14 years, a decline that has been driven, in part, by the fact that a strong El Niño in the late-1990s elevated fire counts to an artificially high level. Also, persistent droughts in some fire-prone parts of Africa and Australia, likely driven by global warming, have left some areas with little fuel to burn, explained Luigi Boschetti, a University of Maryland researcher who has led the effort to develop the mathematical techniques used to detect burn scars.


Climate Change: A Cause and Consequence

To understand climate, its critical that scientists determine how carbon dioxide and other greenhouse gases move among the land, air, and ocean. Since fires release carbon dioxide into the atmosphere and recovering forests and vegetation do the opposite, knowing whats burning around the world and why is central to understanding and modeling climate change.


MODIS has been absolutely critical in pinpointing global fire emissions, said University of California, Irvine fire specialist James Randerson. Better estimates of the frequency, intensity of burning, the area burned, and the type of vegetation burned  characteristics that help define what fire specialists call fire regimes  have been especially important to improving emission estimates.

The last decade of research has shown a regions fire regime can play an enormous role in determining whether a given wildfire ultimately adds carbon to the atmosphere or not. Some of the areas that burn the most frequently, like the grasslands of Africa and Australia, contribute little or no net carbon to the atmosphere because vegetation regrows so rapidly.


In addition, peat fires release about ten times as much of the potent greenhouse gas methane and five times as much carbon dioxide as savanna fires do. As a result, fires in Russia, Canada, and Indonesia  nations that have some of the largest quantities of peat in the world  contribute disproportionately to climate change.




Theres unfortunately no simple rule. We expect to see a range of responses depending on local conditions, Randerson said. In relatively moist areas that are getting drier and warmer, such as the boreal forests in North America and Asia, climatologists expect  and have already observed with MODIS  signs that fires are growing larger and burning more intensely.



Air Quality: Perfecting Smoke Plume Predictions






The EPA relies upon a modeling system that predicts the movement of plumes of air pollution called the Community Multi-scale Air Quality (CMAQ) model. Until just a few years ago, CMAQ only included crude estimates of wildfire smokes contribution to the overall problem.

One of the most significant accomplishments of NASAs Applied Sciences Program has been to convince the Environmental Protection Agency of the value of using MODIS fire data in the CMAQ model, which is used for national decisions associated with air quality, explained Soja who has worked closely with the EPA to integrate MODIS data into the model.

The inclusion of MODIS fire data about the location of actively burning fires has markedly improved CMAQs ability to predict dangerous levels of air pollution. In addition, air quality forecasters use near-real-time MODIS data to improve local and national air quality forecast. Accurate early warnings are critical, Soja noted, because they give people the option to reduce their risk of exposure to poor air by limiting outdoor activity or filtering their air.

Still, much can be done to improve the model. One of the most important problems remaining with CMAQ, Soja said, is the simplicity of the technique thats currently used to estimate the height of smoke plumes. Large, hot-burning fires tends to inject smoke far higher into the atmosphere than smaller fires do, and estimating plume height incorrectly results in inaccurate projections of where smoke ultimately ends up.

Soja and colleagues at Langley are currently using data from a number of satellites and instruments, including MODIS, in an attempt to improve CMAQs plume height estimates. She expects that better plume heights, as well as more accurate estimates of agricultural fire emissions, will be incorporated into the EPAs model within the next two years.

Fire Management: Harnessing Data in Near Real Time

Prior to MODIS reaching orbit, forest managers lacked the space-based view that many now take for granted. Were really living in the golden age of remote sensing and mapping, said U.S. Department of Agricultures Forest Service remote sensing specialist Everett Hinkley.





With VIIRS on the new NPP satellite poised to begin delivering data about wildfires into operational systems in the coming months, scientists at NOAA and the University of Maryland are working aggressively to ensure that the transition to VIIRS data goes smoothly. There are important differences between the instruments that we need to be prepared to handle, said NOAA scientist Ivan Csiszar, a member of NASAs NPP Science Team and the person leading the effort to ensure data continuity between MODIS and VIIRS. But I expect that VIIRS will extend the global fire record long into the future.

Note by GFMC: NASA Releases Visual Tour of Earth’s Fires

NASA has released a series of new satellite data visualizations that show tens of millions of fires detected worldwide from space since 2002. The visualizations show fire observations made by the MODIS instruments onboard NASA’s Terra and Aqua satellites:
