## 3 Results  
### Spatiotemporal Patterns of Drought from 2000 to 2022  
Over the past two decades, the overall trends in the SPI, SPEI, and TVDI were generally consistent (Figure 2), all of which are suitable for regional drought assessment. However, the spatial resolution of the SPI is 5.57 km, whereas that of the SPEI is 0.50\({}^{\circ}\), which can be used for large-scale drought monitoring. In contrast, the TVDI, with a spatial resolution of 1 km, offers greater accuracy and applicability for small-scale study areas. Therefore, in this study, TVDI was used to analyze drought stress conditions and their impact on vegetation ecosystems in Guilin city.  
The annual average TVDI in 2022 reached 0.5, indicating mild drought conditions. Although the TVDI values in 2004 (0.53), 2008 (0.55), and 2017 (0.51) were greater than that in 2022, the differences were minor, all within the range of mild drought conditions. Specifically, the average TVDI reached 0.6 from July to December, indicating moderate drought, it consistently remained above 0.76 from August to November, indicating moderate to severe drought, and it exceeded 0.8 in September 2022, indicating severe drought. Therefore, the Guilin City Emergency Management Bureau issued a warning for localized severe hydrological drought in 2022 [33], indicating its severity and concentration in terms of historical records.  
In addition, we used the 2020-2021 period, with an average TVDI value of 0.46 (a normal drought category), as the baseline period for comparing and analyzing the responses of regional vegetation ecosystems to drought stress in 2022.  
The spatiotemporal distribution and trend of drought in 2022 in Guilin city are shown in Figure 3. The proportion of drought-affected areas in the karst areas is significantly higher than in the non-karst areas. Under the impact of the drought event in 2022, the proportion of drought-affected areas in karst areas was greater than that in non-karst areas (Figure 3). A total of 66.23% of the karst areas exhibited mild drought, 13.04% exhibited severe drought, and 16.80% exhibited drought. In contrast, 31.06% of the non-karst areas exhibited mild drought, 21.83% exhibited severe drought, and only 2.48% exhibited drought, indicating that karst areas more notably exhibited moderate and severe drought stress conditions than non-karst areas did in 2022.  
Drought conditions in karst areas have been intensifying over time (Figure 4a). This conclusion is supported by the 95% confidence interval test (Figure 4b), indicating that karst areas are more sensitive to drought stress compared to non-karst areas from 2000 to 2022. Lower \(CV\) values were mainly concentrated in karst areas and their adjacent subareas (Figure 4c), suggesting that karst areas have been persistently experiencing drought stress over time, with limited adaptability compared to non-karst areas.  
Figure 3: Spatial distribution of the TVDI in 2022, the black line represents the karst area.  
Figure 2: Drought trend analysis in Guilin city based on the standardized precipitation index over 12 months (SPI-12), standardized precipitation evapotranspiration index over 12 months (SPEI-12), and TVDI.