Ecohydrological interactions and landscape response to recent hydroclimatic events in Australia

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Amplification of the water cycle as a consequence of climate change is predicted to increase the climate variability as well as the frequency and severity of droughts and wet extremes over continents such as Australia. Australia has recently experienced three large-scale hydroclimatic extremes, including a decadal millennium drought from 2001 to 2009 (termed the 'big dry'), followed by a short wet pulse during 2010 and 2011 (termed the 'big wet'), and another continent-wide dry condition in 2015. These dry and wet events exerted pronounced negative impacts on water resources, natural ecosystems and agriculture over large areas of Australia. Despite these extreme hydroclimatic impacts, the fate of ecohydrological resources such as the loss and recovery of water storage and vegetation remain largely unknown. The overall goal of this thesis is to study the ecohydrological interactions and landscape response to Australia's early 21st century hydroclimatic extremes. To achieve thesis objectives, I (1) firstly investigated the spatial partitioning and temporal evolution of water resources across Australia under extreme hydroclimatic impacts, (2) then assessed the associations between the climate variability and dynamics in water resources and vegetation productivity, (3) furthermore examined the resilience of regional arid ecosystems to the highly variable water regimes and large-scale hydrological fluctuations, and (4) conducted a synthesized assessment of ecohydrological variations and interactions under these dry and wet events at continental, regional and biome scales, respectively. Results show that highly variable continental patterns were observed in water resources and vegetation, involving differences in the direction, magnitude, and duration of total water storage and surface greenness responses to drought and wet periods. These responses clustered into three distinct geographic zones that correlated well with the influences from three large-scale climate modes: the El Niño-Southern Oscillation (ENSO), the Indian Ocean Dipole (IOD) and the Southern Annular Mode (SAM). At regional scale, ecosystems such as arid wetlands exhibit strong ecological resilience to hydroclimatic extremes, and are presumably sensitive to future altered water regimes due to climate change. In addition, Total Water Storage Anomaly (TWSA) data derived from Gravity Recovery And Climate Experiment (GRACE) satellites was found to be a valuable indicator for ecohydrological system performances and effectively linking the extreme climate variability with Australia's ecosystems. This thesis highlights the value of Remote Sensing techniques (e.g. GRACE satellites) as important tools for improved assessments and management of water resources and associated ecosystems in Australia, particularly in the face of future increasing hydroclimatic extremes.
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