# Response of Grassland Vegetation Growth to Drought in Inner Mongolia of China from 2002 to 2020
## 3 Results
### Changes in Drought from 2002 to 2020  
Figure 5 indicates the SPEI and standardized anomaly of CCI-SM (SA\({}_{\text{CCI-SM}}\)) change trends from 2002 to 2020 in Inner Mongolia grassland. As shown in Figure 5, SPEI values exhibited frequent fluctuations at the times of 1 month (SPEI-1) or 3 months (SPEI-3), while remaining relatively stable at longer time scales (SPEI-12). The pronounced amplitude and higher frequency of wet and dry changes were primarily associated with SPEI-1 (Figure 5a). From 2002 to 2020, Inner Mongolia grassland experienced a total of 96 drought months, including 50 mild, 33 moderate, 12 severe, and 1 extreme drought months. Among these,  
Figure 4: Spatial patterns and change trends of grassland NDVI (**a**,**e**), EVI (**b**,**f**), COSIF (**c**,**g**), and GPP (**d**,**h**) with 0.05\({}^{\circ}\) spatial resolution in Inner Mongolia between 2002 and 2020.  
the lowest SPEI-1 value (\(-2.05\)) was recorded in March 2019 (Figure 5a). In contrast, SPEI-3 exhibited greater stability and provided insight into seasonal-scale dry-wet changes. During the same period, a total of 119 drought months were recorded, comprising 54 mild droughts, 48 moderate droughts, 14 severe droughts, and 3 extreme droughts. The lowest SPEI-3 value (\(-2.08\)) occurred in June 2017 (Figure 5b). SPEI-12, reflecting the annual-scale dry-wet variation, was the most stable among the three indices. From 2002 to 2012, SPEI-12 identified 57 mild droughts, 71 moderate droughts, 23 severe droughts, and 6 extreme droughts. The lowest SPEI-12 value (\(-2.11\)) was found in March 2018 (Figure 5c). In particular, SPEI-3 values were observed as \(-1.34\), \(-1.45\), \(-1.42\), and \(-1.33\) in June, July, August, and September 2007, respectively, and \(-2.08\) and \(-2.0\) were observed in June and July 2017, respectively (Figure 5b). The soil moisture status of Inner Mongolia grassland was identified using SA\({}_{\text{CCI-SM}}\) (Figure 5d). From 2002 to 2020, a total of 112 drought months were identified using the soil moisture (SA\({}_{\text{CCI-SM}}\) \(<0\)), with the minimum value of SA\({}_{\text{CCI-SM}}\) appearing in December 2020 (SA\({}_{\text{CCI-SM}}\) = \(-2.54\)). Notably, from June 2007 to September 2007, SA\({}_{\text{CCI-SM}}\) values consistently fell below \(-1\) in Inner Mongolia grassland. Specifically, in June, July, August, and September 2007, SA\({}_{\text{CCI-SM}}\) values were \(-1.59\), \(-1.30\), \(-1.71\), and \(-1.91\), respectively. In June and July 2017, SA\({}_{\text{CCI-SM}}\) values were \(-1.02\) and \(-1.12\), respectively (Figure 5d). Considering droughts indicated by SPEI-3 and SA\({}_{\text{CCI-SM}}\), June 2007 to September 2007 and June 2017 to July 2017 were selected to analyze the response of grassland vegetation growth to droughts. Figures 6 and 7 present the spatial patterns of SPEI-3 and SA\({}_{\text{CCI-SM}}\) in Inner Mongolia grassland for June, July, August, and September 2007 and June and July 2017. As illustrated in Figure 6, the percentage of grassland areas affected by severe and extreme drought was 47.98%, 59.24%, 63.01%, and 64.16%, respectively (Figure 6a-d). These regions are primarily situated in the central eastern part of Inner Mongolia, with milder drought conditions observed in the western regions. The spatial distribution of SA\({}_{\text{CCI-SM}}\) closely mirrored that of SPEI-3. The proportion of areas with SA\({}_{\text{CCI-SM}}\) values less than \(-1\) was 61.38%, 48.37%, 41.31%, and 54.23%, respectively (Figure 6e-h). In June and July 2017, 61.27% and 56.36% of the grassland area showed extreme drought conditions, concentrated in the central eastern part of the western part of  
part of Inner Mongolia (Figure 7a,b). The spatial distribution of SA\({}_{\text{CCI-SM}}\) closely paralleled that of SPEI-3, with proportions of areas experiencing SA\({}_{\text{CCI-SM}}\) values less than \(-1\) at 50.80% and 45.70%, respectively (Figure 7c,d).