During the period from 1997 to 2009, Australia experienced a severe and persistent drought known as the millennium drought (MD). Major water shortages were reported across the continent, and there were some field accounts of tree mortality and dieback, but large-area assessment has been lacking. Given uncertain projections of future drought conditions in South-East Australia, analysis of the MD presents a valuable opportunity to assess possible impacts of these future trends. In this study, we analyzed the magnitude and sensitivity of vegetation responses to the MD with satellite-derived information including the fraction of photosynthetically absorbed radiation, photosynthetic vegetation cover, canopy density derived from vegetation optical depth, and aboveground biomass carbon. Results show that the most severe impacts were concentrated in southeastern Australia where all four biophysical variables exhibited the highest absolute declines. Cultivated lands, followed by grasslands, experienced the largest drought impact and also demonstrated the highest sensitivity to drought compared to natural biomes. Shrublands showed the greatest resistance to drought-induced declines. Forests exhibited the lowest sensitivity in canopy properties but average drought sensitivity for biomass, similar to other natural biomes. More arid settings tended to have higher drought sensitivity for canopy properties but lower sensitivity to biomass loss. Drought-induced carbon releases were largest in forested ecosystems and in more humid climatic settings. High sensitivity of forest biomass to drought suggests that a large amount of carbon could be vulnerable to release to the atmosphere.
Bibliographical noteFunding Information:
This work was supported by NASA Headquarters under the NASA Earth and Space Science Fellowship Program (Grant 17F-0236). This research was partially supported by the Australian Government through the Australian Research Council's Linkage Projects funding scheme (Project LP140100232). M. D. K. acknowledges support from the ARC Discovery Grant (DP190101823), the Australian Research Council Centre of Excellence for Climate Extremes (CE170100023), and the NSW Research Attraction and Acceleration Program. Data sources used in this study could be accessed with references in Table. Data and codes used for this study could be obtained from the website (https://doi.org/10.5281/zenodo.3445515).
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- carbon cycle
- Drought extremes
- remote sensing
- time series