Weakening sensitivity of global vegetation to long-term droughts

Droughts have dramatic direct and indirect impacts on vegetation and terrestrial ecosystem stability, including decreases in growth and subsequent decreases in CO2 absorption. Although much research has been carried out on the response of vegetation to droughts, it remains unclear whether biomes are becoming more resistant or more vulnerable to drought. In this study, we used the Standardized Precipitation Evapotranspiration Index (SPEI, a multiscalar drought index) and the Normalized Difference Vegetation Index (NDVI, an indicator of vegetation growth) to detect the sensitivity of vegetation growth to droughts across 12-24 month timescales and to detect the change in this sensitivity over recent decades. We found that vegetation growth was most sensitive to 17-18 month droughts in water-limited regions, implying pronounce legacy effects from water conditions in previous years. In addition, we detected reduced coupling between drought and vegetation growth, probably caused by release moisture stress in water limited areas. Meanwhile, we observed a shortening of drought timescale to which vegetation most sensitively responded from an average of 18.1 to 17.2 months, suggesting the weakening of the drought legacy effect on vegetation growth. Results of this study contribute to the overall understanding of the resistance and resilience of ecosystems to drought conditions.