# Satellite-Observed Global Terrestrial Vegetation Production in Response to Water Availability
## 5 Conclusions  
In this study, we explored satellite-observed global terrestrial vegetation production in response to water avaliability by determining global vegetation productivity's seasonal dynamics in response to drought in various climate zones and land biomes and quantifying its vulnerability under predictable drought scenarios. Our primary conclusions are as follows:  
1. Different LUE models have a good fit effect in estimating GPP. The fitting R\({}^{2}\) of VPD\({}_{\text{GLO}}\)-SM, VPD\({}_{\text{MOD}}\)-SM, VPD\({}_{\text{GLO}}\)-ETR and VPD\({}_{\text{MOD}}\)-ETR were 0.7739, 0.7399, 0.7427, 0.7459 and 0.7628, respectively. From 1982 to 2015, the global mean annual GPP of terrestrial vegetation continued to increase at an average rate of 0.134 Pg C a \({}^{-1}\) (\(p<0.001\)), but its growth rate declined after the mid-1990s. GPP is expected to decrease in 71.91% of the global land vegetation area because of increases in radiation and temperature and decreases in soil moisture during drought periods. 2. Vegetation productivity and water availability are largely correlated positively globally. Further, seasonal changes also affect vegetation productivity's dependence upon water availability. The correlation coefficient between GPP and SPEI declined from 0.76 to 0.47 as the climatic conditions became gradually humid, indicating that the vegetation productivity in arid and semiarid areas depends more heavily on water availability than that in humid and semi-humid areas. Various land cover types have different adaptation strategies to the increase and loss of water resources, and the productivity of GRA, SAV, and DBF has a higher correlation with water availability. * 3. 56.8% of the global terrestrial ecosystems' response time to water resources is based primarily on short and medium-term time scales (3-6 months). The GPP's mean response time to SPEI increased from 3.9 to 8.9 months as the climatic conditions became gradually humid, which indicates that the capacity of productivity of vegetation in arid and semiarid areas to withstand long-term water shortages is weaker than that in humid and semi-humid areas. The land cover types that are more relevant to water availability are often accompanied by weak drought resistance, while DNF, OS, EBF and WET have a stronger ability to resist long-term water deficits. * 4. Under the scenario of the same level of GPP damage with different drought degrees, as droughts increase in severity, GPP loss probabilities increase as well. Further, under the same drought severity with different levels of GPP damage, drought's effect on GPP loss probabilities weakens gradually as the GPP damage level increases. Similar patterns were observed in different seasons. Our results showed that arid and semiarid areas have higher conditional probabilities of vegetation productivity losses under different drought scenarios. The productivity loss probability of EBF, DNF, OS, SAV, and GRA show an increasing trend in different seasons, and different land types have different responses to drought in different seasons.