Structural stability of vegetation greening across India from multi-season MODIS EVI: a time–frequency earth observation framework

Abstract

Large-scale vegetation greening has been widely reported across India; however, national assessments have largely relied on monotonic trend metrics without explicitly evaluating seasonal variability, spatial heterogeneity, or the structural persistence of vegetation dynamics. This study presents a physiography-resolved, multi-season assessment of vegetation change using a 24-year (2001–2024) MODIS 16-day Enhanced Vegetation Index (EVI; 250 m) dataset spanning 14 physiographic subdivisions. Seasonal Mann–Kendall analysis and Sen’s slope estimation reveal widespread but spatially heterogeneous greening, with all physiographic subdivisions exhibiting significant positive winter trends and the strongest greening rates (0.0032–0.0051 yr⁻¹) over the Central Highlands, Northern Deccan, and Western Coastal Plains. Pixel-scale analysis indicates significant greening over 62.47 % of India during the pre-monsoon and 61.46 % during winter, declining to 34.57 % during the monsoon before partially recovering (∼43 %) during the post-monsoon, whereas browning remains limited (<2.2 %) and spatially restricted. Complete Ensemble Empirical Mode Decomposition with Adaptive Noise (CEEMDAN) further reveals that vegetation dynamics across most physiographic subdivisions are dominated by sub-interannual (6–24 month) variability, indicating that long-term greening is embedded within persistent low-frequency oscillations rather than short-term fluctuations. In contrast, high-frequency variability is concentrated over climatically extreme and hydroclimatically stressed regions. Seasonal Intrinsic Mode Function 3 (IMF3) energy anomalies identify monsoon-concentrated, off-monsoon-amplified, and mixed variability regimes, while a persistence-based stability metric demonstrates that statistically significant greening does not necessarily imply structural resilience. The Western Plain exhibits the highest structural persistence, whereas plateau, mountain, and humid eastern regions remain dominated by temporal instability despite positive greening trends. By integrating seasonal trend analysis, frequency-resolved decomposition, physiographic stratification, and land-use differentiation, this study provides a scalable Earth observation framework for distinguishing persistent vegetation regime from variability-dominated change across heterogeneous landscapes.