## 3 Results  
### Characteristics of Atmospheric Droughts, Soil Droughts, and Compound Droughts  
The SVPDI trend showed an upward trajectory from 2001 to 2010, followed by a decline. This temporal pattern reflects a pre-2010 phase of atmospheric drying followed by a post-2010 period of wetting (Figure 3a). When viewed across the entirety of the 2001-2020 period, the atmosphere showed a subtle increase in moisture levels (Figure 3a) with a distinct drying trend within the GS (Figure 3b). The rates of change are \(-0.007\)/decade for the entire observation period and \(0.224\)/decade during the GS. Con  
Figure 2: Flowchart illustrating the methodologies utilized in this study. versely, the SSMI showed a significant upward trend on both annual and GS timescales throughout 2001-2020, indicating a wetting trend of the soil in the TRHR. The annual SVPDI showed a clear increasing trend in the western parts of the TRHR (>0.5/decade) and a clear decreasing trend in the eastern parts of the TRHR (<\(-0.5\)/decade) (Figure 4a,b). This spatial differentiation underscores a discernible shift towards dryness in the western parts of the region, accompanied by a pronounced tendency towards wetness in the eastern parts. The spatial trends of the GS SVPDI were generally similar to those of the annual SVPDI, but the areas characterized by wetting trends shrank in the eastern parts while areas marked by drying trends expanded in the western parts (Figure 4c,d). The annual SSMI showed a clear decreasing trend (<\(-0.5\)/decade) in the central and eastern regions of the TRHR and a clear upward trend (>0.5/decade) in most of the remainder of the region (Figure 4e,f). These changes suggest that the soil is trending wetter in most areas of the TRHR, with a tendency to become drii  
Figure 3: (**a**) Annual and (**b**) GS changes in SVPDI and SSMI in the TRHR during 2001–2020. The blue and red solid lines indicate the changes in SVPDI and SSMI, respectively. areas. The spatial trends of the GS SSMI are generally similar to those of the annual SSMI (Figure 4g,h). The spatial durations of the annual (Figure 5a) and GS (Figure 5b) atmospheric droughts were generally similar, with longer durations in the southern parts of the TRHR. Soil droughts with relatively long duration occurred mainly in the eastern parts of the TRHR, at up to 5 months/year (Figure 5c) and 2 months/year (Figure 5d) on the annual and GS timescales, respectively. Annual compound droughts generally lasted from 1 to 2.5 months/year (Figure 5e), while GS compound droughts generally lasted from 0.3 to 1.2 months/year (Figure 5f). Areas with lengthy annual compound droughts reaching 2 months/year were distributed throughout the western and southern parts of the TRHR. The spatial durations of GS compound droughts were broadly similar to those of annual compound droughts, but generally longer in southern and eastern parts. Figure 4: Spatial distribution of (**a**,**b**) annual and (**c**,**d**) GS SVPDI trends in the TRHR during 2001–2020. Spatial distribution of (**e**,**f**) annual and (**g**,**h**) GS SSMI trends in the TRHR during 2001–2020. The statistical significance was identified at \(p<0.05\). As depicted in Figure 6a, the atmospheric drought duration increased more intensely on the GS timescale (0.23 months/decade) than on the annual timescale (0.11 months/decade). We estimated the trends of atmospheric drought durations during equal time periods (2001-2010 and 2011-2020) to further analyze trend characteristics across distinct temporal divisions. For both the annual and GS timescales, the atmospheric drought showed significant increasing trends from 2001 to 2010 (6.35 months/decade on the annual timescale and 2.61 months/decade on the GS timescale), which reversed in 2011 and markedly decreased from 2011 to 2020 (\(-\)1.63 months/decade on the annual timescale and \(-\)1.08 months/decade on the GS timescale). The more recent decreasing rates of atmospheric droughts were substantially smaller than the increasing rates before 2011.