Assessing Urban Green Infrastructure Transformation in Delhi (1991–2021): A Landscape Ecology and Remote Sensing Approach

Urban green spaces (UGS) play a crucial role in ensuring ecological stability and improving the quality of life in rapidly urbanizing regions. This study investigates the long-term transformation of UGS in the National Capital Territory of Delhi (NCTD), India, over a three decades (1991–2021), a time marked by unprecedented urban expansion. Multi-temporal Landsat satellite imagery was used for analysis, including Landsat 5 TM (1991, 2001), Landsat 8 OLI (2011), and Landsat 9 OLI-2 (2021). An unsupervised classification was carried out using the ISODATA clustering algorithm in ERDAS Imagine software to classify six major land use/land cover (LULC) categories. Change detection matrices were also constructed to analyze land transitions across three decadal intervals and cumulatively over the entire study period. Landscape and class-level metrics (PLAND, PD, LPI, LSI, COHESION, CONTAG, SHDI, and SHEI) were computed to assess changes in landscape structure and spatial configuration. Results show a significant increase in built-up area (from 263.18 to 570.56 km²) primarily at the expense of agricultural land, vegetation, and open space. Forest cover demonstrated a net gain in the final decade, likely reflecting restoration efforts and reclassification, while vegetation showed consistent fragmentation and loss. The CONTAG index revealed increasing spatial aggregation, while SHDI and SHEI declined, indicating reduced landscape diversity and evenness. Class-level metrics revealed rising patch density and geometric irregularity in vegetation and forest classes, suggesting ecological fragmentation. The findings highlight the urgent need for integrated urban planning, policy reform, and proactive monitoring strategies to mitigate the ecological consequences of unbalanced urban growth. This research provides valuable insight for sustainable green space management in megacities undergoing intense land transformation.