###### Abstract  
Satellite-estimated solar-induced chlorophyll fluorescence (SIF) is proven to be an effective indicator for dynamic drought monitoring, while the capability of SIF to assess the variability of dryland vegetation under water and heat stress remains challenging. This study presents an analysis of the responses of dryland vegetation to the worst extreme drought over the past two decades in Australia, using multi-source spaceborne SIF derived from the Global Ozone Monitoring Experiment-2 (GOME-2) and TROPOspheric Monitoring Instrument (TROPOMI). Vegetation functioning was substantially constrained by this extreme event, especially in the interior of Australia, in which there was hardly seasonal growth detected by neither satellite-based observations nor tower-based flux measurements. At a 16-day interval, both SIF and enhanced vegetation index (EVI) can timely capture the reduction at the onset of drought over dryland ecosystems. The results demonstrate that satellite-observed SIF has the potential for characterizing and monitoring the spatiotemporal dynamics of drought over water-limited ecosystems, despite coarse spatial resolution coupled with high-retrieval noise as compared with EVI. Furthermore, our study highlights that SIF retrieved from TROPOMI featuring substantially enhanced spatiotemporal resolution has the promising capability for accurately tracking the drought-induced variation of heterogeneous dryland vegetation. dryland; SIF; EVI; TROPOMI; extreme drought +
Footnote †: journal: remote sensing  
0000-0002-319-788X][PERSON] 0000-0002-0002-3199][PERSON]  
0000-0002-3199-788X][PERSON]. 0000-0002-3199-788X][PERSON]. 0000-0002-3199-788X]J.J.H. 0000-0002-3199-788X]M.  
as well as the 2012-2013 drought over arid inland [4; 5]. Australia tends to be a global hot spot for variability, with semiarid vegetation in that country exhibiting increased carbon uptake [6]. By persisting through the 'big dry' and responding favorably in a following 'big wet' [7], Australia's ecosystems play a significant role in regulating the global water and carbon cycles [4]. Enhancing our understanding with respect to dryland ecosystem in response to climate extreme is paramount for effectively managing the environment and global change research [8; 9; 10; 11]. Satellite-based observation offers a method for monitoring and characterizing the spatiotemporal dynamics of vegetation under changing climates [12], which is especially valuable for remote areas such as most Australia's interior with very sparse monitoring sites. Traditional reflectance-based vegetation indices are widely applied to assess the effects of extreme drought on ecosystem functioning and vegetation productivity at a regional, continental, or global scale [8; 13; 14; 15; 16; 17]. Dramatic impacts of climate extremes on vegetation dynamics (as measured by EVI) with abrupt changes in phenology and productivity over southeast Australia demonstrates that semiarid ecosystems exhibit the largest sensitivity to hydro-climatic variations [18; 19]. Although vegetation-index-based approaches are essential for evaluating vegetation variation under large-scale drought events, the observations they provide are not directly associated with vegetation functioning [20]. During recent years, satellite retrievals of SIF based on energy reemitted directly from the core of photosynthetic machinery present a fresh manner to observe vegetation growth and response [21; 22; 23]. On account of energy conservation, variations in SIF signal include information regarding vegetation physiological, biochemical, and metabolic functions in addition to the amount of absorbed photosynthetically active radiation [20]. Numerous studies have examined the relationship between GPP and SIF for each biome at various scales retrieved from different satellite sensors [24; 25; 26; 27], implying that SIF can be unbiased in monitoring of vegetation productivity and further contribute to the understanding of the global terrestrial carbon cycle [28; 29].