The strengthened impact of water availability at interannual and decadal time scales on vegetation GPP.

Water availability (WA) is a key factor influencing the carbon cycle of terrestrial ecosystems under climate warming, but its effects on gross primary production (E ) at multiple time scales are poorly understood. We used ensemble empirical mode decomposition (EEMD) and partial correlation analysis to assess the WA-GPP relationship (R ) at different time scales, and geographically weighted regression (GWR) to analyze their temporal dynamics from 1982 to 2018 with multiple GPP datasets, including near-infrared radiance of vegetation GPP, FLUXCOM GPP, and eddy covariance-light-use efficiency GPP. We found that the 3- and 7-year time scales dominated global WA variability (61.18% and 11.95%), followed by the 17- and 40-year time scales (7.28% and 8.23%). The long-term trend also influenced 10.83% of the regions, mainly in humid areas. We found consistent spatiotemporal patterns of the E and R with different source products: In high-latitude regions, R changed from negative to positive as the time scale increased, while the opposite occurred in mid-low latitudes. Forests had weak R at all time scales, shrublands showed negative R at long time scales, and grassland (GL) showed a positive R at short time scales. Globally, the E , whether positive or negative, enhanced significantly at 3-, 7-, and 17-year time scales. For arid and humid zones, the semi-arid and sub-humid zones experienced a faster increase in the positive E , whereas the humid zones experienced a faster increase in the negative E . At the ecosystem types, the positive E at a 3-year time scale increased faster in GL, deciduous broadleaf forest, and savanna (SA), whereas the negative E at other time scales increased faster in evergreen needleleaf forest, woody savannas, and SA. Our study reveals the complex and dynamic E at multiple time scales, which provides a new perspective for understanding the responses of terrestrial ecosystems to climate change.