Spatiotemporal dynamics of dryland vegetation photosynthesis and greenness under hydroclimatic extremes

University of Technology Sydney. Faculty of Science.Australia’s dryland ecosystems play a critical role in regulating the climate system and considerably influence the interannual variability in global carbon cycle. However, the dynamics of dryland vegetation under climate variability and extreme events have not been as thoroughly investigated as in other ecosystems. Spaceborne solar-induced chlorophyll fluorescence (SIF) provide a fresh means to evaluate vegetation photosynthetic activity and detect vegetation stress. Considering its spatially coarse resolution, studies with reference to the application of SIF over heterogeneous dryland ecosystem are rarely reported. The main goal of this thesis is to explore the spatial and temporal dynamics of Australia’s dryland vegetation under hydro-climatic extremes using satellite-estimated fluorescence and greenness. To achieve this goal, I first utilized a strong wet pulse in 2016-2017 as well as in the 2011 big wet period as natural experiments to assess the response of major dryland biomes in central Australia. Next, I investigated the impact of a recent extreme drought on spatiotemporal variability of Australia’s dryland vegetation indicated by multi-source satellite-based SIF. Finally, I analysed the spatial pattern and seasonal variations in dryland vegetation phenology under climate variability. The results showed semiarid ecosystems to have the largest variability and were most sensitive to climate extremes. SIF derived from the Global Ozone Monitoring Experiment-2 (GOME-2) at 0.5 spatial resolution has an insufficient capacity for capturing spatiotemporal dynamics over xeric central Australia as a result of low signal level and high retrieval noise. In contrast to humid ecosystems, both SIF and enhanced vegetation index (EVI) simultaneously captured the declines of arid/semiarid plant growth from the beginning of extreme drought events at 16-day scale. SIF data retrieved from TROPOspheric Monitoring Instrument (TROPOMI) at a 0.05 spatial grid exhibits promising capability of mapping and characterizing the dynamics of heterogeneous dryland vegetation in future. This thesis highlights that the incorporation of satellite-observed greenness and fluorescence can potentially contribute to an improved understanding of dryland vegetation dynamics and can advance our ability to detect ecosystem alterations under future changing climates