Climate Extremes Reshape Carbon Uptake in India: A Multi-Scale Assessment of Vegetation–Climate Interactions

Extreme climate events are increasingly altering biosphere–geosphere exchanges, particularly through their impacts on vegetation productivity and carbon uptake. In this study, we evaluate how multi-dimensional climate extremes shape the spatiotemporal dynamics of Gross Primary Productivity (GPP) across India, a region characterized by strong hydroclimatic variability and rapidly changing land–atmosphere feedbacks. We used FLUXCOM-X GPP estimates (0.25°, 2001–2021) and ERA5-based meteorological variables to derive key climate extremes indices including temperature extremes (TX10P, TX90P), vapor pressure deficit extremes (VPDX90P), soil moisture extremes (SMX10P), and extreme precipitation indicators (RX5day, R20mm). Long-term changes in vegetation productivity were quantified using the Mann-Kendall test and Sen’s slope estimator, while wavelet power spectrum (WPS) and wavelet coherence (WTC) analyses were employed to explore dominant periodicities of GPP variability and its coupling with extreme climatic drivers at seasonal, annual, inter-annual, and long-term timescales. Results reveal widespread increasing trends in GPP across India over the past two decades, driven primarily by intensification of monsoon-season productivity. However, seasonal analysis identifies emerging constraints during the dry season, reflecting the increasing dominance of evaporative stress and atmospheric water demand on vegetation functioning. The impacts of extremes are strongly heterogeneous: heat and VPD extremes exhibit a pronounced negative influence on GPP in central and semi-arid zones with limited water availability; cold extremes reduce productivity in northern and northeastern ecosystems with winter-dominated phenology; soil moisture deficits consistently suppress carbon assimilation across all vegetated systems, while wet anomalies provide strong productivity enhancement; and intense precipitation events generally increase GPP by alleviating moisture stress except in temperate northern regions and north-eastern parts of India, where intense flooding and lower temperatures suppress net growth. Dominant annual cycles in croplands highlight strong synchronization with monsoon-driven growing seasons, whereas forests dominated regions demonstrate inter-annual to long-term modes, reflecting deeper rooting strategies, structural inertia, and ecological memory. WTC results indicate that GPP coherence with high temperature, VPD extremes and low soil moisture extremes is frequently strong and negative, suggesting that future warming and humidity stress may offset current productivity gains. Meanwhile, positive coupling with precipitation extremes implies a growing reliance of ecosystem carbon uptake on episodic wet events. Overall, the findings demonstrate that intensifying climate extremes are actively reshaping the carbon cycle in India by altering both the magnitude and stability of vegetation productivity. As land–atmosphere interactions become increasingly governed by high-impact events rather than gradual change, monitoring multi-scale GPP response and ecosystem sensitivity will be crucial for predicting future terrestrial carbon feedbacks and supporting climate-resilient land management strategies in vulnerable tropical and subtropical regions.