# The Resilience of Vegetation to the 2009/2010 Extreme Drought in Southwest China
## 4 Discussion
### Limitations and Perspectives  
Estimation of the influences of extreme drought on vegetation critically relies on the data sources used [57]. However, remote sensing data have some common shortcomings, for example, the measurement is indirect; electromagnetic waves can be contaminated by clouds or aerosols during transmission, resulting in dead pixels; and there are artifacts associated with sensor malfunctioning [58]. In addition, NDVI, LAI, and GPP have their own shortcomings, for example, a significant limitation of NDVI is the saturation effect at high levels of vegetation cover [30]. When estimating the LAI of needleleaf forest, shoot clumping is not taken into account [31]. Furthermore, the algorithm used to estimate GPP has the limitation of the inappropriate characterization of light use efficiency [59], which may lead to an inaccurate estimation of resilience.  
At present, there are many drought indices that can be used to characterize extreme drought, for example, extreme drought can be quantified based on the changes in environmental factors (such as precipitation and temperature) or vegetation indices (such as NDVI and the enhanced vegetation index (EVI)) [60]. Moreover, the effects of extreme drought events on vegetation are related with the season. [PERSON] et al. [18] revealed that vegetation growth and productivity decreased during the 2009/2010 winter-spring extreme drought, but were enhanced during the 2011 summer drought in SWC. [PERSON] and [PERSON] [61] also found that extreme drought did not always inhibit vegetation and its influence on vegetation was related to the local hydroclimate in China. In future studies, multiple drought indices can be used to describe the characteristics of extreme drought and the effects of different drought events on vegetation resilience should be compared.  
In SWC, the government has implemented some ecological protection projects, such as the Natural Forest Protection Project and the Grain for Green Program [62]. Vegetation coverage and productivity in SWC has been improved and previous studies have indicated that the mean annual NDVI, LAI, and GPP in SWC showed an increasing trend from 2000 to 2018, with rates of 0.003, 0.04 m\({}^{2}\) m\({}^{-2}\), and 10.58 g C m\({}^{-2}\), respectively [35]. Since human activities greatly influence vegetation growth and productivity [63], they should be considered in future studies. However, it is not always easy to distinguish between natural and human-induced environmental factors, because the occurrence of extreme drought events and the accompanying changes in meteorological variables are linked to human-driven climate change.  
Our results showed that the NDVI and LAI values of vegetation in SWC were able to recover by more than 80% within 5 months. However, the vegetation showed low growth after the extreme drought. Thus, we should not ignore the negative impact of extreme drought on vegetation growth and productivity. Government managers can formulate appropriate policies to better cope with extreme drought, such as protecting local vegetation, supporting precise agriculture irrigation, and maintaining and planting highly drought-resilient plants.