Analysis of net primary productivity trends in india by incorporating the direct effect of CO ₂ fertilization in MODIS data

Abstract India is the second-largest contributor to global greening. Despite significant increase in green cover, satellite-based MODIS estimates reveal no significant increase in vegetation productivity, with major forested areas showing declines in net primary productivity (NPP), due to warming. A major limitation of MODIS vegetation productivity dataset is that it does not consider the improved biochemical rate of plant photosynthesis under higher atmospheric CO 2 levels, known as CO 2 fertilization (CFE). In this study, we incorporate the direct effect of CFE into satellite-based MODIS vegetation productivity estimates and reassess NPP trends across India from 2001 to 2024. Our analysis confirms that the NPP trend values nearly doubled after accounting for the direct effect of CFE, significantly reducing the percentage of grids exhibiting a negative trend from 21.21% to 8.86% across total vegetated land and from 51.81% to 25.23% across forested land, compared to the trends observed without CFE. Notably, most of the grids showing negative trends transitioned into statistically non-significant categories, either negative or positive. These grids are primarily located along the Western Ghats and southern peninsular India, where vegetation productivity showed only a modest increase in response to the direct effect of CFE. This limited response is likely due to concurrent warming in these regions, which dampens the benefits of CFE. In contrast, northwestern India, where atmospheric moisture stress and temperature have declined, exhibited a stronger increase in vegetation productivity after accounting for CFE — enhancing already positive trends. Overall, our findings suggest that incorporating the direct effect of CFE significantly improves the estimation of vegetation productivity trends across India. However, regional climate patterns have a strong influence on the magnitude of the increase in vegetation productivity due to the direct effect of CFE. This study enhances understanding of climate-vegetation interactions under increasing atmospheric CO 2 concentration and climate change.