Harnessing green infrastructure for urban heat island mitigation: Evidence-based strategies for sustainable and climate-resilient cities

• Identify persistent UHI effects despite population decline. • Observe multi-year and seasonal UHI variations in Dwa cold climate zone. • Challenge assumption that summer SUHII always exceeds winter SUHI. • Prove GIF more accurate than NDVI for vegetation coverage. • Recommend diversified greening strategies for dense, declining urban contexts. The urban heat island (UHI) effect poses a significant environmental and public health challenge, particularly in the context of climate change. While urban green infrastructure (UGI) is widely recognised for its cooling potential, its implementation and effectiveness in complex, high-density urban environments, especially in extremely cold climate cities, require a comprehensive multi-scale assessment. This study presents a holistic framework that integrates seasonal variability, socioeconomic transitions, and spatial heterogeneity to evaluate UHI mitigation strategies. Drawing on satellite imagery (Landsat and MODIS), land use surveys, socioeconomic regression analysis, and computational fluid dynamics (CFD) simulations using ENVI-MET 4.0, the study identifies UHI hotspots and assesses incremental, space-efficient greening interventions. A longitudinal case study (2000–2020) in a severely cold climate city in northeast China reveals that population decline did not reverse UHI or UGI trends, as the extent of built-up areas remained largely unchanged. The findings demonstrate that green roofs provide significant cooling benefits in high-density urban settings while also enhancing thermal regulation during winter months. By integrating analyses across multiple scales, this research offers a robust methodology for quantifying UHI mitigation potential and informing data-driven urban greening strategies. The study refines vegetation metrics using land survey data, challenges assumptions about seasonal UHI dynamics, and highlights the urgent need for targeted green infrastructure in both growing and shrinking urban contexts. Overall, the research contributes to a deeper understanding of green retrofitting in extreme climates and identifies future directions for policy development, design optimisation, and interdisciplinary approaches to climate-resilient urban planning.