## 3 Results and Discussion
### Spatial and Temporal Variation of Drought in NEC Based on CDI  
The spatial pattern of the CDI trends in the NEC growing season was obtained by using Sen's slope and the MK significance test in three time periods: 1982-2020, 1982-1999, and 2000-2020, and the statistics were conducted by vegetation type (Figure 7). This analysis revealed that while there was clear spatial heterogeneity in CDI trends across time periods, there was some similarity between the different months of the growing season. During 1982-2020 (Figure 7a), the CDI primarily decreased in the western part of the study area, while it increased in the central and eastern parts. There, CDI significantly decreased in the western part of the study area in July, August, and September, with the largest number of significantly decreasing grid points in August. CDI trends were mostly downward throughout the study area, but in farmland (Figure 7d), the proportion of grids with decreasing trends decreased with each passing month, from 64.6% in May to 30.0% in September, with mainly downward trends (becoming dry) in May and June, and mainly  
Figure 6: Temporal variation of drought-affected area of agriculture and different drought indices for farmland in NEC, 1986–2015. (The scPDSI value typically ranges from \(-4\) to \(4\), and here it is divided by \(4\). )upward trends (becoming wet) from July to September. The trend of CDI in the study area shifted significantly around 2000 (Figure 7b-d), with farmland, woodland, and grassland cover areas dominated by a non-significant decrease from 1982 to 1999 and a significant increase from 2000 to 2020. However, some of the regional CDI trends remained consistent in both time periods, while the southwestern region of the study area experienced an upward trend in CDI during various months of the growing season during both periods, whereas the northwestern and southeastern regions experienced an opposite trend. The range of CDI trends for both periods before and after 2000 was higher than that of 1982-2020 (Figure 7a-c), indicating that later wetting suppressed the trend of drying throughout the period. Areas of significant changes in CDI trends over the three time periods were mostly found in farmland and grassland areas, indicating that dry/wet conditions and vegetation growth in these areas are more susceptible to climate change. According to the drought levels classified by the CDI, the spatial distribution of drought frequencies of varying severity during the growing season in NEC from 1982 to 2020 is presented (Figure 8). The results showed that the frequency decreased with increas  
Figure 7: Spatial pattern (**a**–**c**) and statistics (**d**) of CDI trends during the growing season in NEC at different periods. (Dotted area indicates an MK significance test of \(|Z|>1.96\); the upper part of the bar graph indicates the proportion of the grid with an increasing trend, and the colored part indicates the proportion of the grid with significant change.) ing drought intensity. May and June had more drought occurrences than July through September. The western and eastern regions of the study area have a high frequency of light drought, while the central farmland and southern grassland regions have a high frequency of moderate, severe and extreme drought. Severe and extreme drought disasters rarely occur in woodlands. On the one hand, forest ecosystems are complex and have a high stability of resistance [48], and on the other hand, the CDI is a short-term drought monitoring indicator, which is more suitable to reflect agricultural drought. The impact of different levels of drought during the growing season of farmland and grassland in NEC from 1982 to 2020 (Figure 9) showed that agricultural drought events in different months of the growing season were mainly concentrated in 2000-2009, with light and moderate drought dominating before 2000 and after 2009, and the impact scope of severe and extreme drought increasing greatly from 2000 to 2009.