Increased Sensitivity of Global Vegetation Productivity to Drought Over the Recent Three Decades

Intensified droughts have been weakening global vegetation productivity, yet how the sensitivity of vegetation productivity to drought changes over time is not well known. Here, using the simulated long-term gross primary production (GPP) with an improved two-leaf light use efficiency model and the Standardized Precipitation Evapotranspiration Index (SPEI), we studied the sensitivity of global vegetation productivity to drought, quantified by the corresponding time scale of SPEI with strongest drought impact on GPP, and analyzed the changes in the sensitivity over two time periods (1993-2005 and 2006-2018). Compared to the first period, droughts were more widespread and severer around the world in the second period, as evidenced by increased drought range (increased by 4.43%) and intensity (SPEI03 decreased by 103%). Globally, the area with significant correlation between GPP and SPEI increased by 25.53%, the impact intensity increased by 14.75%, and the drought sensitivity of GPP enhanced by 13.76%; the changing directions were pretty similar across various vegetation types, mostly showing an increasing trend. Moreover, the vegetation in regions with consistently decreasing moisture was affected by drought most strongly and experienced the greatest change in the sensitivity of GPP to drought (enhanced by 10.99%), indicating that the arid and semi-arid ecosystems should be considered as a research priority in the future. Our results reveal strengthened drought sensitivity of global vegetation productivity in recent decades across various ecosystems and climate transition regions, which could improve our understanding on the behavior and fate of terrestrial ecosystems in the changing climate.