Strategic urban greening for UHI mitigation across local climate zones in Lahti, Finland : a transferable framework with multi-criteria analysis and microclimatic simulations

Abstract

The Urban heat island (UHI) effect is an emerging concern in cold-climate cities as climate change accelerates, with Lahti—a city in Finland—experiencing record-breaking summer temperatures and increased heat stress in recent years. This study develops and demonstrates a systematic, transferable framework for strategic urban greening, integrating multi-criteria analysis and microclimatic simulations to identify, prioritize, and evaluate greening interventions across local climate zones (LCZs). The framework is designed to support evidence-based decision-making and can be adapted to other urban contexts facing similar challenges. The research mapped UHI patterns in Lahti using remote sensing and field measurements. LCZ classification revealed that compact midrise (LCZ 2) and large low-rise (LCZ 8) areas consistently exhibited the highest surface and air temperatures, with the hottest built-up zones averaging 5.8°C warmer than the coolest natural areas, and nocturnal UHI effects reaching 3.2°C. Suitability mapping, based on a multi-criteria analysis, incorporated environmental, technical, and social indicators, such as land surface temperature, vegetation cover, land availability, and population vulnerability, to assess and rank sites for urban greening. This analysis identified the urban core, market square, train station forecourt, and major pedestrian corridors as priority areas for intervention, while areas near forests and water bodies showed low suitability for additional greening. Shadow analysis and solar radiation study using ArcGIS Pro and microclimatic simulations using ENVI-met were conducted in selected high-risk areas. Shadow and solar radiation analysis highlighted significant microclimatic differences between adjacent streets, with open boulevards and squares suffering from high solar exposure and low thermal comfort, while tree-lined streets and courtyards benefited from substantial cooling. While ENVI-met results demonstrated that targeted increases in tree cover and strategic placement of vegetation can reduce mean radiant temperature (MRT) by up to 8°C and improve the Universal Thermal Climate Index (UTCI) by 6–8°C in exposed public spaces giving pedestrians substantial relief from heat stress. The study concludes that a data-driven approach to urban greening, combining fine-scale spatial analysis, stakeholder engagement, and integration with broader urban planning, is essential for effective UHI mitigation. The developed framework is scalable and transferable, providing a clear methodology for prioritizing interventions for heat mitigation that can be applied in both cold and warm climate cities.