## 3 Results  
### Seasonal and Inter-Annual Variations over Local Sites  
Figure 3 shows the inter-annual variations in eddy-covariance-estimated GPP and satellite-based SIF, EVI over five selected flux sites during 2014-2019. Generally, both satellite variables, especially EVI, exhibited the capacity for capturing the seasonal and inter-annual dynamics of dryland vegetation as indicated by tower-based GPP (\(r^{2}\) ranging from 0.47 to 0.86). Compared with northern mesic sites, the two southern semi-arid sites (AU-ASM, AU-TTE) displayed much higher inter-annual variability, of which there was no seasonality detected by satellite observation nor field measurement in 2018-2019 (Figure 3d,e). Likewise, there was significant hysteretic senescence in EVI as opposed to GPP and SIF over two southern sites, in particular in the wet year of 2016-2017 (Figure 3d,e). The POS of SIF was mostly advanced relative to those of EVI. Furthermore, we found that multi-year series of GOME-2 SIF were more erratic and deviated from the fitted SSA-reconstructed curves than GPP and EVI across northern humid sites, as well as southern arid sites. Figure 2: Schematic diagram of phenological metrics’ retrieval. The curve refers to the seasonal SSA-re-reconstructed EVI or SIF profile at a daily scale. SOS: the start of the growing season; POS: the peak of the growing season; EOS: the end of the growing season; RSP: the rate of spring green-up; RAU: the rate of autumn senescence. To assess the ability of SIF and EVI to track the seasonal dynamics of dryland vegetation as delineated by tower-based GPP, mean seasonal cycles of vegetation variables (normalized to unity at the maxima) over five selected tower sites during 2014-2019 are shown in Figure 4. For northern mesic site AU-How, GOME-2 SIF indicates a consistent  
Figure 3: Time series of SSA-reconstructed tower-based GPP, GOME-2 SIF, MODIS EVI over **(a)** AU-How, **(b)** AU-Dry, **(c)** AU-Stp, **(d)** AU-ASM, and **(e)** AU-TTE. R-squared (\(r^{2}\)) refers to the relationship between GPP and EVI (green) and GPP and SIF (orange), respectively. Vertical dashed lines refer to the peak of the growing season in each hydrological year. growing season with tower data, in contrast to the 1-2-month lagged seasonal profile of EVI during both the green-up and senescent periods (Figure 4a). Conversely, a notably advanced springtime increase and earlier autumn drop are observed in SIF relative to tower-based GPP and EVI for the AU-Dry site (Figure 4b). For three semi-arid and arid sites (AU-Stp, AU-ASM, AU-TTE), both GPP and SIF show a slightly narrower mean seasonal profile as opposed to two northern sites (Figure 4c-e). Besides, there is substantial later senescence in EVI as compared with GPP, SIF, and APAR (\(\approx\)EVI\(\times\) PAR) over southern water-limited sites. Likewise, the seasonal profiles of APAR significantly shifted 1-2 months earlier relative to those of EVI over all selected sites. The differences of key phenological metrics (SOS and EOS) derived from satellite-observed SIF and EVI as compared with tower-based GPP over five flux tower sites during 2014-2019 are presented in Table 1. For SOS over three northern sites (AU-How, AU-Dry, and AU-Stp), the mean absolute errors (MAE) of both SIF and EVI ranging from 7 to 32 days were generally less than those over two southern arid sites (AU-ASM and AU-TTE, ranging from 31 to 54 days). On the contrary, there was a larger discrepancy in EOS at AU-How and AU-Dry (MAE ranges from 39 to 60 days). Besides, for two southern sites (AU-ASM and AU-TTE), the differences of EOS between EVI and GPP were notably larger than those between SIF and GPP. Figure 4: (**a–e**) Seasonal cycle (mean) of tower-based GPP, GOME-2 SIF, MODIS EVI, and EVI \(\times\) PAR over 5 selected local sites during 2014–2019. Curves are normalized with respect to unity at the maximum annual value. (**f**) Seasonal cycle (mean) of PAR over 5 selected local sites during 2014–2019.