Increasing Atmospheric Aridity Moderates the Accelerated Rate of Vegetation Green-Up Induced by Rising CO2 and Warming

Abstract

The rate of vegetation green-up (RVG) indicates the ability of vegetation to respond to changes in climatic conditions. Understanding long-term RVG trends can clarify the changes in how quickly the vegetation grows from dormancy to maturity with time. However, how RVG trends respond to environmental variables and variable interactions remains unknown. We examined the long-term RVG trends (1981–2018) over the northern extratropics and determined the influence of environment variables and interactions between variables on the RVG trends based on the Global Land Surface Satellite leaf area index and a multivariable regression considering interactions between variables (MRCI). Our results showed a persistent increase in RVG at 0.020% (8-day)−1 year−1 over the entire region. Except for shrublands (−0.032% (8-day)−1 year−1), RVG trends increased significantly, particularly in woody savannas (0.095% (8-day)−1 year−1) and mixed forests (0.076% (8-day)−1 year−1). The relative importance of interactive effects (RIIAE) to the RVG trends is roughly 30%. Rising CO2, enhanced vapor pressure deficit (VPD), and warming are the primary factors affecting the RVG trends, both at the pixel and the biome scales. The accelerated RVG is triggered by both rising CO2 and warming but is partially offset by increased VPD. Our findings shed light on the relative contribution of variable interactions and assessed the relationship between environmental factors and RVG trends across different biomes, hence strengthening our knowledge of vegetation spring green-up in response to global change.