## 3 Results  
### Spatiotemporal Dynamics of the 2018-2019 Extreme Drought  
From the start of the new century, there was a significant increase trend in the total area influenced by extreme dry condition and an opposite trend in the region-wide mean SPEI (\(p\)-value < 0.0001). The extreme, 4-month drought spanning from December 2018 to March 2019 was the worst drought event during the last two decades over central and northwest Australia (Figure 2), of which almost the entire region was influenced by this event (Figure 3a). During the 2018-2019 monsoon season, a total area of 1.75 million km\({}^{2}\) was under extreme dry condition extending from north to xeric central Australia (15\({}^{\circ}\)-26\({}^{\circ}\)S and 118\({}^{\circ}\)-138\({}^{\circ}\)E), particularly in December 2018 and January 2019. In addition, the xeric inland experienced a longer extreme dry period (more than 2 months) relative to the mesic northern coastal regions (Figure 3b). Temporal variations in satellite-based SIF, SIF\({}_{\text{PAR}}\), EVI, and GPP averaged within the extent of extreme and medium dry, respectively, are displayed in Figure 4. Compared with approximately one standard deviation (SD) decline in all vegetation variables under medium dry, those exhibited 2-3 times SD decrease relative to climatology under extreme situation. Correspondingly, both SIFPAR and EVI showed the largest reduction from January 2019 as a consequence of persistent rainfall deficit as well as increased temperature since November 2018. Spatial patterns of standardized anomalies of precipitation, surface/root zone soil moisture, LST, SIF, SIF\({}_{\text{PAR}}\), EVI, and GPP during the 2018-2019 monsoon season are shown in Figure 5, along with the corresponding pixel density classified by extreme and medium dry. Meteorological data show that 87%, 25% of study region appeared rainfall anomalies below than \(-1\) SD, \(-2\) SD, respectively, and 91%, 60% of the area exhibited air temperature anomalies larger than 1 SD and 2 SD, revealing it was a large-scale drought event coupled with an extreme heatwave (Figure 5a,d). The persistently reduced precipitation along with higher temperature results in depletion of both surface and root zone soil water content over most areas, of which 70%, 50% showed less than \(-\)1 SD, respectively (Figure 5b,c). Figure 3: (**a**) Spatial pattern of drought intensity based on SPEI6-month during 2018–2019 monsoon season. (**b**) Pixel-wise number of extreme-dry months based on SPEI1-month. Four pairs of ROIs are shown in Figure 3a. The black boundary represents the extent of extreme (within) and medium (outside) dry. Figure 2: (**a**) Time series of the total area under extreme dry within the extent of study region during 2000–2019. Red line refers to the linear regression line. (**b**) Region-wide mean monthly SPEI6-month during 2000–2019. (**c**) Region-wide mean monthly SPEI1-month during 2018–2019. Figure 4: The spatially averaged seasonal cycles of monthly EVI, GPP, SIF, and \(\text{SIF}_{\text{PAR}}\) within (**a,c,e,g**) medium and (**b,d,f,h**) extreme dry extent from July 2018 to June 2019. The grey curves represent the monthly multiyear mean (2007–2018). Vertical lines refer to \(\pm 1\) standard deviation. Figure 5: (**a–h**) Spatial distributions of the standardized anomalies of precipitation, surface/root zone soil moisture, LST, SIF, \(\text{SIF}_{\text{PAR}}\), EVI, and GPP during 2018–2019 monsoon season. (**i–l**) Pixel density of four vegetation variables within the extent of extreme and medium dry. Vegetation growth is largely affected by the extreme drought, and the majority of the area showed negative anomalies for all vegetation variables relative to the multiyear mean (Figure 5e-h). \(\text{SIF}_{\text{PAR}}\) and EVI exhibited a similar spatial pattern, where those were remarkably negative anomalies (\(<\)\(-\)2 SD) between 17\({}^{\circ}\)-20\({}^{\circ}\)S and 129\({}^{\circ}\)-138\({}^{\circ}\)E (Figure 5f,g).