# Satellite-Observed Global Terrestrial Vegetation Production in Response to Water Availability
## 3 Results
### Spatio-Temporal Dynamics of Vegetation Productivity's Dependence on Water Availability  
The monthly LUE GPP series was correlated with the SPEI of multiple time scales (1-24 months) to determine the extent to which water resources determine global vegetation productivity changes. As shown in Figure 4a, vegetation productivity and water availability are largely correlated positively globally, indicating that vegetation productivity tends to increase (decrease) as water supply increases (decreases). In 47.30% of the global terrestrial ecosystem, the correlation coefficient between GPP and SPEI can exceed 0.6. Particularly in the Southwest United States, Southeastern Argentina, South Africa, Central Asia, and Australia, the correlation coefficient between GPP and SPEI can exceed 0.8, indicating that vegetation productivity in these areas depends more upon water supply. Seasonal changes also affect the correlation between GPP and SPEI. As Figure S3a-d shows, the regions with a high correlation between GPP and SPEI in the United States and Central Asia were located primarily in the Southwest of these two regions in March-May, and from June to August, the scope and intensity of GPP that SPEI affected in these two regions reached the maximum (the correlation coefficient was 0.6 or higher). As the rainy season in the Northern hemisphere fades, the correlation between GPP and SPEI in the United States and Central Asia weakens gradually, and from December to February of the following year, the correlation coefficient between GPP and SPEI in this region fell below 0.4. Vegetation productivity and water availability's dependence in the high latitudes of the Northern hemisphere is relatively stable, and remains largely between 0.2 and 0.4, while the correlation between GPP and SPEI in Australia is strong throughout the year.  
As shown in Figure 5a, an analysis of the changes in the correlation between GPP and SPEI in various climate zones indicated that as the climatic conditions become gradually  
Figure 4: Geographical patterns of vegetation productivity’s dependence upon, and response to, water availability. (**a**) Spatial distribution of the maximum correlation coefficients recorded between LUE GPP and SPEI in each pixel during 1982–2015. (**b**) SPEI timescales at which the maximum correlation coefficient between LUE GPP and SPEI was found over the period 1982–2015.  
Figure 3: Geographic distributions of potential climate factors (temperature, radiation and soil moisture) to GPP from 1982 to 2015.  
hould, the dependence between vegetation productivity and water availability continues to decrease (the correlation coefficient between GPP and SPEI declined from 0.76 to 0.47). Different seasons showed consistent characteristics, indicating that the vegetation productivity in arid and semiarid areas is more sensitive to changes in water availability than in humid and semi-humid areas. By comparing the maximum correlation coefficients of GPP and SPEI under different land cover types (Figure 6a), it can be seen that the productivity of GRA, SAV and DBF has a greater correlation with water availability (the correlation coefficients are 0.69, 0.64 and 0.61 respectively), followed by CRO, MF, DNF, ENF, OS and EBF (correlation coefficients of 0.57, 0.55, 0.53, 0.51, 0.50, and 0.50 in order). WSA and WET's productivity had the weakest correlation with water resources. Our results showed that various land cover types have different adaptation strategies to the increase and loss of water resources.