# The Ongoing Greening in Southwest China despite Severe Droughts and Drying Trends
## 4 Discussion  
Drought events in SWC from 2009 to 2012 have been widely reported in previous studies. Vegetation was damaged during this period, which is also reflected in our research. Some previous studies used different drought indices to quantify the severity of these drought events in different regions of SWC and also showed the same spatial pattern as this study, which emphasized the necessity of subregional research on the impact of drought events on vegetation [17; 32]. When the temperature is higher than the optimal temperature for vegetation growth, it may reduce the photosynthesis and carbon sequestration capacity of the vegetation [33]. During drought events, LAI, EVI, and GPP all have a clear decrease trend in drought areas, but comparing LTT and ADT, it can be found that the greening of vegetation recovers quickly after drought events. Generally speaking, moisture and temperature conditions after drought are the key factors that affect the time of vegetation restoration. Humid conditions will further accelerate vegetation restoration, while drought conditions will prolong vegetation restoration [34; 35]. In addition, some recent studies have shown that the global drying trend has affected the growth of vegetation. After 2000, most of the global vegetation has experienced a transition from greening to browning (greening slows down) [36; 37]. However, we found an interesting phenomenon in our research; while experiencing drought events, a very obvious drying trend was found throughout SWC--vegetation continued to green and productivity also significantly increased. Long-term vegetation trends only had a slight impact in heavy drought areas, and basically no impact in slight drought areas. In other words, the vegetation quickly recovered to the pre-drought level after the drought event (Figure 11). This may be the result of the joint effect of climate change and human activities. Partial correlation analysis shows that temperature is the main driving factor for vegetation greening in the SWC (Table 3), which means that although SWC is undergoing a drying process, precipitation still meets the vegetation's growth needs. For areas where there is no limit of water, climate warming stimulates the growth of vegetation by extending the growing season and promoting photosynthesis in summer [38]; a similar study took place in the Amazon forest. Due to the increase in solar radiation, the extreme drought in 2015/2016 did not affect the greenness of the vegetation. There even was an increase in greening rate--21.6% of the forest experienced a rise [39]. Figure 10: The annual trend regression residuals of vegetation indicators, temperature, and precipitation. (**a**–**c**) represent LAI, EVI, and GPP respectively; all pixels that do not meet the prerequisites (\(R^{2}>0.3\), \(p<0.05\)) and the residuals that are not significant have been removed. The vegetation restoration time depends on the severity of the drought, the climatic conditions after the drought, and so on. Although climate change is an important driving factor for vegetation greening, only relying on the effects of climate change after experiencing severe drought events may not show vegetation restoration (Figure 11 II or Figure 11 III); thus, we believe that land management is another important factor in the rapid restoration of vegetation in this area after drought. The SWC has experienced extensive land-use changes, which will also cause changes in vegetation. A previous study showed that large-scale ecological projects in SWC have led to a broad increase in the leaf area index and above-ground biomass, which is in sharp contrast to the negative trends found in the ecosystem model simulation without human influence [40]. Similar studies have also shown that China and India contributed more than one-third of the observed net increase in global green leaf area through land management [25]. Similar to these studies, the role of land management in this area is very significant.