Unveiling the Mechanisms and Implications of Vegetation Carbon Dynamics for the last two decades in India

Abstract

In recent decades, vegetation cover and productivity exhibit substantial variability around the globe. Both climate drivers and human induced changes significantly impact vegetation, which is not adequately explored for the Indian region. Here, we use satellite and reanalysis data to unravel the phenomena driving the greening/browning of India. The analysis shows that India is largely greening (62.5%) and marginally browning (14.1%). This greening is predominantly by the contribution of croplands (72.3%), led by Zaid (70.1%), followed by Kharif (59.5%) and Rabi (54.8%) agricultural seasons of India. Among the climate drivers, soil moisture (44%) has the major influence followed by temperature (32%) and precipitation (23%). Greening is predominantly observed in the north west due to positive influence of both increased soil moisture and decreased temperature, termed as the ‘moisture induced greening’. The Indo-Gangetic plain (IGP) is the most extensively irrigated region in the world, which results in greening. Drying due to warming and increased soil heat flux, termed as the ‘warming induced moisture stress’, suppresses Gross Primary Productivity (GPP) (i.e., browning), mainly in the croplands of southern India and eastern IGP. Granger causality test reveals that warming induced moisture stress is taking place at a lag of 1 month in these areas. We also examined the Carbon Use Efficiency (CUE), a metric to define the ability of plants to sequester carbon from atmosphere, of vegetation in different regions. Water availability as soil moisture (32%) and precipitation (26%) has strong positive influence on CUE, establishing its importance in driving vegetation carbon dynamics (VCD) for cropland dominated India. Our analysis shows enhanced productivity (greening) in regions of lower (< 0.3) CUE in western India (moisture induced greening) and IGP (irrigation induced agricultural boom). However, a reduced productivity (browning) is found in the northeast, east (deforestation and extreme events) and south (warming induced moisture stress) India in regions of higher (> 0.6) CUE, which is a concern. Effective management of croplands and conservation of forest resources is the key to achieve sustainable development goals (SDGs). Furthermore, it serves as a tool to counter the challenges of food security, global warming and climate change.

Keywords: Greening; Browning; Vegetation carbon dynamics (VCD); Soil Moisture; Food security; Climate Change