# Response of Grassland Vegetation Growth to Drought in Inner Mongolia of China from 2002 to 2020
## 3 Results
### NDVI, EVI, GOSIF, and GPP Loss at Different Drought Levels  
In order to evaluate the impact of different drought severity levels on grassland vegetation, we examined the NDVI, EVI, GOSIF, and GPP reductions across varying drought severities in Inner Mongolia. In general, all levels of drought (moderate, severe, and extreme) led to a decline in NDVI, EVI, GOSIF, and GPP (Table 2). However, the extent of NDVI, EVI, GOSIF, and GPP reductions varied significantly. For NDVI, the average reductions caused by moderate, severe, and extreme droughts were 8.82%, 14.46% and 26.81%, respectively. Similarly, EVI exhibited average reductions of 8.71%, 15.04%, and 27.11% under moderate, severe, and extreme drought conditions, respectively. Notably, GOSIF showed much larger reductions in the grassland of Inner Mongolia, with reductions of 20.58%, 22.83%, and 67.31% under moderate, severe, and extreme droughts, respectively. For GPP, the average reduction caused by moderate, severe, and extreme droughts was 10.52%, 18.01%, and 27.05%, respectively. Overall, NDVI, EVI, GOSIF, and GPP exhibited decreased significant declines with increasing drought severity, with GOSIF displaying the most pronounced response to drought.  
Figure 11: Temporal variation of NDVI (**a,b**), EVI (**c,d**), GOSIF (**e,f**), GPP (**g,h**), and SM (**i,j**)during the May to October drought in 2017. \(\Delta\) is the different between values of monthly NDVI, EVI, GOSIF, and GPP in May, June, July, August, September, and October 2017 and multi-year monthly average values of NDVI, EVI, GOSIF, GPP, and SM from 2002 to 2020.  
The reductions in NDVI, EVI, GOSIF, and GPP across various grassland types along the drought severity gradient exhibited notable differences (Figure 12). During extreme drought conditions, the most significant NDVI reductions were observed in TS, with an average loss of \(-31.54\%\). LM, TMS, and TSD also experienced substantial NDVI reductions, with averages of \(16.88\%\), \(-16.52\%\), and \(-27.37\%\) (Figure 12a). A similar pattern was observed for EVI reductions, where TS, LM, TMS, and TSD exhibited reductions of \(-31.69\%\), \(-17.25\%\), \(-20.45\%\), and \(-25.30\%\), respectively (Figure 12b). Remarkably, GOSIF reductions were most pronounced in TS, with an average loss of \(-92.15\%\), followed by LM, TSD, and TMS (Figure 12c). Regarding GPP, TS experienced the highest average loss (\(-32.29\%\)), followed by TSD, TMS, and LM (Figure 12d). For severe drought conditions, GOSIF reductions in TS, LM, TMS, and TSD were \(-65.83\%\), \(-53.23\%\), \(-33.96\%\), and \(-53.94\%\), respectively (Figure 12c). GPP exhibited average losses of \(-23.42\%\), \(-15.40\%\), \(-15.28\%\), and \(-16.87\%\), in TS, LM, TMS, and TSD, respectively (Figure 12d). These findings highlight the significant variation in NDVI, EVI, GOSIF, and GPP reductions across different grassland types within the context of the same level of drought. TS displayed the most substantial decrease ratio, while TMS exhibited the smallest decrease ratio.  
We also assessed the reductions in NDVI, EVI, GOSIF, and GPP across TS in June and July 2017. The most significant TS reductions were observed in GOSIF and GPP in June 2017. The average loss of GOSIF and GPP was \(-39.04\%\) and \(39.14\%\) during extreme drought conditions and \(-23.09\%\) and \(-17.9\%\) during severe drought (Figure 13a). Similar results were also found for July 2017: the average loss of GOSIF and GPP was \(-40.39\  
and 46.51% during extreme drought conditions and \(-\)9.84% and \(-\)8.99% during severe drought (Figure 13b).