Shifts in Climatic Limitations on Global Vegetation Productivity Unveiled by Shapley Additive Explanation : Reduced Temperature but Increased Water Limitations

Abstract

Global fluctuations in vegetation productivity are intricately tied to climatic variability, but how climate change will alter climatic limitations on productivity is unclear. Here, we used shapley additive explanation (SHAP), a novel technique based on game theory, for identifing the contributions of climatic factors to vegetation productivity. We also delineated climatic limitations on productivity and traced their temporal evolution during 1982-2018 using the SHAP values. The results identified that, in temperate, boreal, and polar zones, temperature primarily limited productivity during the early growing season, and temperature and radiation jointly limited productivity during the peack and late growing season. In contrast, water and radiation predominantly limited productivity mainly in arid and equatorial zones, respectively. We also observed an alleviated temperature but an intensified water limitations on productivity across different months. The alleviated temperature limitation was particularly notable in June for the northern hemisphere (July for the southern hemisphere), with the temperature-constrained area decreasing significantly at a rate of 2.2‰/y (1.2‰/y). In contrast, the exacerbation of water limitation was most pronounced in June (September), with the water-constrained area expanding significantly at a rate of 2.8‰/y (3.3‰/y). Our findings underscore the imperative for a more explicit incorporation of the impact of water limitation in understanding regional and global carbon dynamics under a warming climate.