Scientists Measure Impacts of Fire and Other Disturbances
on North American Boreal Forest Biomass
Leveraging NASA Center for Climate Simulation (NCCS) and Boston University (BU) high-performance computing resources, academic researchers analyzed 31 years of satellite data to measure how disturbances including fire and timber harvests have impacted the aboveground biomass (AGB) in North American boreal forests.
Undertaken for NASA’s Arctic-Boreal Vulnerability Experiment (ABoVE), the study covered an area stretching 2.82 million square kilometers (1.09 million square miles) across western Canada and Alaska (see map below).
“Previous studies have observed widespread ‘greening’ of Arctic-boreal ecosystems,” explained Jonathan Wang, Postdoctoral Scholar, Department of Earth System Science, University of California, Irvine, who initially led the study while a doctoral student at BU. “However, frequent and extensive disturbances, such as fires, threaten carbon stocks and can mask actual carbon gains.”
The new study recently appeared in the journal Nature Climate Change. For this research, Wang and his collaborators analyzed 475 billion observations from NASA and U.S. Geological Survey satellites:
|Satellite/Instrument||Instrument Resolution||Years of Coverage|
|70 meters (m)||2003–2009|
Thematic Mapper (TM)
Mapper Plus (ETM+)
Observation data sources included ABoVE’s 186-terabyte Landsat dataset in the NCCS Centralized Storage System. The scientists ran time series analysis algorithms on the data using over 500 computing cores of the NCCS Discover supercomputer and ADAPT Science Cloud, an effort that took several months. Further processing resulted in 70 terabytes of intermediate data products that served as inputs to machine learning algorithms run at BU to yield annual 30-meter-resolution AGB estimates, with a final dataset of about 140 gigabytes.
“There is an overwhelming amount of new satellite data becoming available, allowing us to monitor ecosystems with unprecedented detail and nuance,” Wang said. “I considered how long it would take for me to perform this analysis on my desktop computer, and it was on the order of a couple centuries. Supercomputing resources like the NCCS are enabling a real leap forward in our capacity to ingest and analyze remote sensing data.”
The study team found that over the years 1984–2014 the ABoVE region gained 434 teragrams (478.4 million tons) of AGB. Yet, the prevalence of large fires significantly reduced these gains, which would have been closer to 600 teragrams (661.39 million tons) of AGB. Timber harvests led to additional, although more modest, AGB losses. Wang noted that when considering other ecosystem processes such as fire soil dynamics, it is possible that these Arctic-boreal ecosystems stored nearly zero net carbon.
The researchers also compared their results with those of 27 Earth system models run for the international Coupled Model Intercomparison Project Phase 6 (CMIP6) experiment. Their study showed that on average the CMIP6 models overestimated AGB gains by a factor of three.
“A major reason for this discrepancy was the models’ inability to capture the trends and magnitude in burned areas,” Wang said. “Climate modeling efforts must focus on more accurately capturing fire regimes in order to better understand the near-term evolution of the carbon cycle and — by extension — global climate.”
- Wang, J.A., A. Baccini, M. Farina, J.T. Randerson, and M.A. Friedl, 2021: Disturbance Suppresses the Aboveground Carbon Sink in North American Boreal Forests. Nature Climate Change, 11, 435–441, doi:10.1038/s41558-021-01027-4.
- ABoVE: Annual Aboveground Biomass for Boreal Forests of ABoVE Core Domain, 1984–2014, Oak Ridge National Laboratory Distributed Active Archive Center (ORNL DAAC) for Biogeochemical Dynamics, doi:10.3334/ORNLDAAC/1808.
Jarrett Cohen, NASA Goddard Space Flight Center