###### Abstract
Both SIF and Moderate Resolution Imaging Spectroradiometer (MODIS) GPP respond to water availability in much the same direction beyond their previously determined correlations, although biome-specific distinction remains evident [30]. Relative to traditional vegetation indices (e.g., normalized difference vegetation index, enhanced vegetation index, leaf area index, etc. ), spaceborne SIF or fluorescence yield was found to show an earlier and more significant response to rainfall deficits and heat stress over tropical vegetated region, forest, and cropland at monthly scale [31; 32]. It highlights that SIF is susceptible to both the structural and physiological variations of vegetation and can be beneficial to timely monitor and characterize the development of drought and heatwave [33; 34; 35]. During the extreme drought of 2015-2016 driven by a strong El Nino event, large-scale decoupling of greenness and photosynthesis over Amazon forests was observed by satellite, of which SIF showed a pronounced reduction as opposed to a slight increase of canopy greenness [36]. The magnitude of divergence in greenness and photosynthesis that are related to times of fluctuant soil moisture differ in sign along a tree cover gradient, and those of forested ecosystems display contrasting average responses [37]. Conversely, both greenness and photosynthesis of non-woody semiarid ecosystems exhibiting a strong response to the availability of soil moisture usually alter contemporaneously [37]. To assess the effect of drought-related stress, there is a need for remotely sensed indicators that measure not only how green the plants are, but also to what extent photosynthetic activity is. By investigating the response of vegetation growth to the 2019 extreme heatwave in Australia, [PERSON] et al. [38] concluded that SIF observed by both GOME-2 and Orbiting Carbon Observatory-2 (OCO-2) are more sensitive to water and heat stress than the greenness-based vegetation index (EVI). In addition, OCO-2 SIF exhibits a more pronounced decrease and one-month earlier than GOME-2 SIF, primarily owing to the diverse timing of observations (overpass timing: GOME-2 at near 09:30 a.m. and OCO-2 at 1:36 p.m. local solar time). Nonetheless, this study was conducted with limited baseline years (2015-2019), and it remains uncertain at a relatively coarse scale (1\({}^{\circ}\) spatial resolution and monthly interval) for heterogeneous Australia's dryland vegetation under highly dynamic climate. The newly launched TROPOMI facilitates a considerable enhancement in SIF observation as a result of unprecedented spatial resolution (up to 7 km \(\times\) 3.5 km at nadir) and near-daily global coverage as contrasted with GOME-2 and OCO-2 [26; 39], which enables the assessment of the relationship of SIF-GPP at an ecologically meaningful scale. Characteristic drought time-scale can play a critical role in determining the sensitivity of biome-specific vegetation to drought [40]. Arid and humid biomes mostly respond to short time-scales, while semiarid and subhumid biomes respond to long time scales [40]. The response of the annual crop yield in five main dryland cultivations in the United States to different time-scales of drought is highly spatial variable, of which some crops (e.g., winter wheat) responded to drought at medium to long SPEI time-scales, while other crops (e.g., soybean and corn) responded to short or long drought time-scales [41]. It remains unclear how major biome types of natural dryland vegetation respond to drought at different intensities and time scales. Here, we utilize the large-scale 2018-2019 drought across Australia as a natural experiment to investigate and characterize the spatiotemporal response of dryland vegetation to this extreme event, using multiple-source satellite observations of solar-induced chlorophyll fluorescence and vegetation greenness.