Greening fails to translate into an increase in Net Primary Productivity due to warming constraints in India

Abstract

India has made the second-largest contribution to global greening in the last two decades. However, it is not clear whether this greening has led to an overall increase in net primary productivity and hence carbon uptake potential, given the impact of climate change on vegetation. In this study, using MODIS satellite data for the period 2001–2019, we attempt to find out the extent to which increased greening in India has led to an overall increase in primary productivity in recent decades. Despite a statistically significant increase in the Leaf Area Index (LAI), we found a slightly decreasing trend (not statistically significant) in Net Primary Productivity (NPP) and stable Gross Primary Productivity (GPP) during the 21st century. Our analysis also shows that the NPP of temporally consistent Indian forests shows a significant decreasing trend despite the increase in LAI. Notably, there are spatial differences in the NPP trend, with the regions contributing the most to NPP in India showing a stronger decreasing trend. The regions with a significantly decreasing NPP trend also experienced the strongest warming during the study period. We also used the nonlinear kernel regression method to investigate the temperature response of vegetation productivity in these regions. We observed that photosynthesis in these regions decreased above a certain temperature and respiration became stable, leading to a decrease in NPP. Our analysis shows that climate change, especially the rise in temperature, has already begun to affect vegetation productivity and carbon uptake in Indian forests. The study also conveys the clear scientific message that increased greening does not necessarily lead to increased carbon uptake, especially in a country like India where agriculture is intensifying. This analysis also has significant implications for the scientific analysis of planning to achieve India's net zero emissions pledge by 2070.