## 4 Discussion  
This study systematically analyzed the spatial and temporal dynamics of drought and vegetation responses in Xinjiang from 2000 to 2020, highlighting the ecological challenges faced by this region under global climate change. The SPEI-based climate drought analysis indicated a slight overall intensification of drought across Xinjiang, with the northern R1 and R2 ecological zones experiencing a notable shift from short-term to prolonged drought. In comparison, zones R3 and R4 showed moderate increases in long-term drought, whereas the southern R5 region remained relatively stable in long-term drought patterns. These findings align with those of [PERSON] et al. [37] which observed increasing temperature and precipitation trends at most meteorological stations across Xinjiang from 1980 to 2020, which were particularly pronounced with rising spring temperatures and winter precipitation. In recent years, Xinjiang has experienced several extreme precipitation events [38]. However, despite the increased precipitation, higher temperatures have intensified evaporation, diminishing the water supplementation provided by rainfall. This effect likely drives the intensification of long-term drought trends (as indicated by SPEI-12 and SPEI-24), reflecting cumulative water deficits. This pattern of intensified drought is closely linked to rising vapor pressure deficit (VPD), which increases transpiration rates and reduces stomatal conductance, exacerbating plant water stress [39]. This effect is particularly pronounced in water-limited regions like Xinjiang, further amplifying the adverse impacts on plant physiological activity. In terms of vegetation conditions, both NDVI and SIF generally showed an upward trend, indicating gradual vegetation recovery in Xinjiang against the backdrop of global climate change. However, in densely vegetated areas within certain northern ecological zones (such as R1, R2, and R3), NDVI and SIF exhibited downward trends, likely due to elevated temperatures offsetting precipitation gains, which intensified soil moisture evaporation and inhibited photosynthesis [40]. From the trends observed in NDVI for forested areas (Figure 9), forests in Xinjiang have shown a significant increase in NDVI from 2000 to 2020, likely indicating forest expansion. This trend may primarily result from increased precipitation and higher temperatures creating favorable conditions for forest growth [41]. However, the slight decline in SIF suggests that photosynthetic efficiency might be constrained by environmental stressors, such as drought or heat [27]. This highlights the complex relationship between structural improvement and physiological stress in forests. In other words, this phenomenon may result from the inadequate adaptive adjustment of vegetation to climate change, leading to decreased vegetation activity in some areas. The differences in the responses of NDVI and SIF reflect their distinct ecological significance. NDVI, derived from the reflectance characteristics of vegetation in the red and near-infrared wavelengths, effectively represents canopy structural attributes and their changes. However, its response to environmental stresses, such as drought, tends to lag behind physiological adjustments. In contrast, SIF, as a fluorescence signal emitted during photosynthesis, directly reflects photosynthetic efficiency and physiological activity, making it more sensitive to changes caused by water or heat stress. For instance, under drought conditions, NDVI may still indicate stable canopy greenness, while SIF rapidly detects declines in photosynthetic activity. [PERSON] et al. [42] observed that in a semi-arid grassland, SIF and GPP exhibited a strong correlation during drought conditions (R\({}^{2}\) = 0.79), with SIF variations predominantly driven by physiological regulation, increasing from 19.29% during wet periods to 60.23% during drought.