Drought impacts on Australian vegetation during the millennium drought measured with multisource spaceborne remote sensing

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.