## 3 Results
### Biogeographic Patterns of Vegetation Phenology  
To contrast the difference in the timing of seasonal greening derived from two satellite-based vegetation indicators and assess spatial variability over the NATT, the region-wide phenology maps based on EVI (Figure 5) and SIF (Figure 6) were generated. Besides, three representative years, 2014-2015 (normal year), 2016-2017 (wet year), and 2018-2019 (dry year), were selected to evaluate the impact of inter-annual precipitation variability on vegetation phenology. We found large spatial and inter-annual variations in the timing of key phenology transition dates retrieved from EVI (Figure 5), particularly in the southern arid/semi-arid NATT (18\({}^{\circ}\)S-23\({}^{\circ}\)S). In the extremely dry year of 2018-2019, EVI exhibited no seasonality over nearly the entire southern NATT as compared with detectable phenology in normal and wet years (Figure 5). There is a remarkable lagging trend in key phenological metrics (especially POS and EOS) in 2014-2015 (normal year) and 2016-2017 (wet year) from north to south across the study area, of which Eucalyptus-dominated woodlands distributed in the humid northern NATT started to green-up earlier (September to October). By contrast, the SOS of Acacia-dominated woodlands and Hummock-dominated grasslands distributed in the arid inland was generally 1-2 months behind (November to December). Similarly, the peak and end of the growing season in the south were 2-3 months delayed compared to those in the north during the normal/wet years.  
The spatial patterns of vegetation phenology derived from SIF across NATT are shown in Figure 6. Consistent with the in situ comparison, the key phenological metrics of most pixels derived from SIF were generally earlier than those derived from EVI. There was a contrary spatial pattern in the timing of transition dates between EVI and SIF, in which arid/semi-arid ecosystems over the southern NATT exhibited advanced POS (December to January) and EOS (March to April) as opposed to POS (February to March) and EOS (April to May) over the northern humid area (Figure 6d-h). With reference to the normal/wet years, larger latitudinal changes in the peak of season between the north (11\({}^{\circ}\)S-17\({}^{\circ}\)S) and south (17\({}^{\circ}\)S-23\({}^{\circ}\)S) NATT under the extremely dry condition of 2018-2019 were observed, and fractional pixels in the south were likewise without detectable phenology (Figure 6c,f).  
With the purpose of further contrasting the differences in the seasonal profile derived from SIF and EVI, the relationship between green-up rate and brown-down rate of two satellite-based indicators among four major vegetation types are shown in Figure 7. For the semiarid/arid biomes (Hummock grasslands and shrublands), the majority of pixels displayed considerably higher green-up rates than senescence rates (RSPEV \(>\) 1 RAUEV1), of which the absolute senescence rate ( 1 RAUEV1 ) of Hummock grasslands was mostly less than 0.002 d\({}^{-1}\) (Figure 7a,b). By contrast, for northern sub-humid/humid biomes (Eucalyptus-dominated forests and woodlands and Tussock grasslands), there were notably rapid and comparable rates of green-up and senescence (0.0005-0.004 d\({}^{-1}\)) (Figure 7c,d). On the other hand, RSPSV and RAUSF ranging from 0.002-0.010 nW m\({}^{-2}\) nm\({}^{-1}\) sr\({}^{-1}\) d\({}^{-1}\) had fewer discrepancies in spite of diverse biomes (Figure 7e-h).