Strategic Urban Greening to Mitigate Urban Heat and Pollution Islands: A Nature-Based Approach for the Megacity Kolkata, India

Urbanization poses significant challenges to climate resilience, particularly in rapidly expanding cities like Kolkata in India. The extensive land use and land cover (LULC) changes resulting from unplanned urban growth have intensified urban climatic issues, notably the Surface Urban Heat Island (SUHI) and Urban Aerosol Pollution Island (UAPI) effects. This study investigates the impact of Kolkata's urbanization over the past 20 years (2000–2020), focusing on the interplay between LULC changes and the exacerbation of SUHI and UAPI phenomena. The findings reveal that the transformation of green spaces into built-up and impervious areas has significantly contributed to rising Land Surface Temperatures (LST) and deteriorating air quality. In contrast, regions with higher vegetation cover consistently recorded lower LST, often remaining below 30 °C, even in densely urbanized zones. Keeping temperatures below 30 °C reduces heat stress and mitigates emissions and are essential for achieving global health priorities and the Paris Agreement goal of limiting temperature rise to 1.5°C above pre-industrial levels. This highlights the critical role of urban greening in mitigating these adverse effects. A tailored vegetation strategy is proposed, categorizing urban areas based on road types—national highways, state highways, and residential roads. Using the i-Tree application, the study identifies suitable tree species for urban greening initiatives, considering Kolkata's unique climatic conditions, including temperature, growing season length and height constraints to achieve desired pollutant removal and eight other environmental factors. By aligning greening efforts with these classifications, the study demonstrates how nature-based solutions can effectively reduce SUHI and UAPI impacts while enhancing urban sustainability. This research underscores the importance of strategic vegetation planning to counteract the negative impacts of urbanization in tropical cities like Kolkata. By addressing LULC changes with targeted urban greening measures, cities can enhance their resilience to extreme climatic events and improve overall environmental quality.

Keywords: LULC, SUHI, UAPI, Urban Greening, Nature-Based Solutions