NCCS-Enabled Satellite Data Assimilation Reveals
Vegetation Changes from Massive Australian Bushfires
In late 2019 to early 2020, Australia had a spring and summer that few who experienced it will soon forget. Massive bushfires burned 25 million acres of land, including 21% of the continent’s forests, with devastating impacts on life and property. To better understand how Australia’s unprecedented fire season affected vegetation, NASA Goddard Space Flight Center scientists and international collaborators mounted an experiment at the NASA Center for Climate Simulation (NCCS), assimilating NASA satellite data into a computer model and analyzing the output.
The experiment focused on hard-hit Southeast Australia, which comprises southern Queensland, New South Wales, and part of Victoria (see map at right). The study area is about 1 1/2 times the size of Texas.
NASA satellites that observe Earth’s surface provide researchers with diverse data at different resolutions. For comparison, the researchers separately assimilated three datasets:
- Soil moisture and vegetation optical depth (VOD) from NASA’s Soil Moisture Active Passive (SMAP) satellite at 9-kilometer (km) resolution.
- Moderate Resolution Imaging Spectroradiometer (MODIS) leaf area index from NASA’s Terra and Aqua satellites at 500-meter resolution.
- Climatological VOD averaged across 2015–2019 as a baseline.
These datasets were assimilated into NASA’s Land Information System (LIS) with the NOAH-Multiparameterization (Noah-MP) land surface model running at 1-km resolution over the period April 2015–February 2020.
Using 512 cores on the NCCS Discover supercomputer, the data assimilation runs took four weeks to finish. The experiments produced approximately 1.2 terabytes of data, which were stored on Discover and analyzed using Python and Matplotlib.
“The 20-member model ensemble at 1-km resolution experiment this large domain is a computationally intensive setup,” said Sujay Kumar, study leader and research physical scientist in NASA Goddard’s Hydrological Sciences Laboratory. “These runs would not have been possible without the NCCS resources.”
The experiment reveals that the SMAP satellite can capture the vegetation disturbances from the bushfires, which Kumar said was “a bit surprising given that SMAP data is fairly coarse.” It also shows that the fires led to significant changes in Southeast Australia’s regional hydrology (see the Impact box above).
The study results compare favorably against five thermal remote sensing and in-situ datasets used for evaluation. The research team is currently running similar studies over other fire-prone regions of the world.
- Kumar, S.V., T. Holmes, N. Andela, I. Dharssi, Vinodkumar, C. Hain, C.D. Peters-Lidard, S.P. Mahanama, K.R. Arsenault, W. Nie, and A. Getirana, 2021: The 2019–2020 Australian Drought and Bushfires Altered the Partitioning of Hydrological Fluxes. Geophys. Res. Lett., 48, no. 1, e2020GL091411, doi:10.1029/2020GL091411.
- “Fires Take a Toll on Australian Forests,“ NASA Earth Observatory, Image of the Day for December 13, 2019.
Jarrett Cohen, NASA Goddard Space Flight Center