Influences of Rainfall Pattern Changes on Vegetation Dynamics of Savanna Ecosystems in Australia under Climate Change
- Publication Type:
- Thesis
- Issue Date:
- 2020
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Climate change has significantly influenced the global hydrological processes with rising temperature and elevated CO₂. Rainfall is the most active factor to influence the terrestrial ecosystems, especially with frequent heavy rainfall events in recent decades. Although much research has addressed the relationship between rainfall and vegetation under climate change, the impacts of rainfall pattern changes on terrestrial ecosystems have still not been stated clearly. In this project, we attempted to explore the mechanism of how rainfall pattern changes driving vegetation dynamics of savanna ecosystems in Northern Territory, Australia, where a well-known rainfall gradient is located and provides a natural laboratory for climatic analysis. To investigate rainfall pattern changes, we diagnosed the long-term rainfall pattern changes by analyzing trend, periodicity, abrupt change, and extreme rainfall events based on long-term rain gauge data, describing rainfall conditions over the sub-continent. The findings supported the view that rainfall pattern has significantly changed and especially occurred after the 1970s, illustrated by showing more frequent hydroextremes. We explored the sensitivity of vegetation phenology to rainfall variations from the wet coastal regions to the dry inland regions over different savanna vegetation biomes by retrieving phenological metrics from MODIS enhanced vegetation index (EVI). Results revealed maximum EVI was the most appropriate proxy to represent vegetation growth status and also be sensitive to rainfall variations, even if the sensitivity declined in water sufficient regions. Afterwards, we demonstrated the dominating roles of rainfall patterns in driving vegetation dynamics by evaluating the relative importance between maximum EVI and three decomposed rainfall pattern components, namely, intensity, duration, and frequency. Surprisingly, we noticed the roles of three factors varied along with rainfall gradient, and frequency become the most dominating factor in controlling vegetation dynamics in semi-arid and semi-humid regions. Eventually, we extended our research from ground rain gauge measurements to TRMM satellite precipitation observations to investigate the spatiotemporal variations of rainfall patterns and its influences. We found savanna biomes in semi-humid regions responded to rainfall changes mostly, and the relative importance of rainfall pattern component followed the consistent spatial regime, which has been illustrated by meteorological data. In summary, this study contributes to the deeper understanding of the roles of rainfall pattern changes in dominating vegetation dynamics under different rainfall conditions, and the findings benefit projection and modelling to mitigate the impacts of climate change.
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