Comprehensive analysis of the impact of elevated metro line infrastructure on the urban heat island effect in Chennai: A multi-model approach

Abstract

This study is driven by the essential need to understand the dynamic urban heat island patterns in Chennai, particularly in light of the city’s significant expansion which resulted in the establishment of connectivity through the implementation of the elevated metro line infrastructure project. A notable gap in the current research landscape lies in the exploration of the impact of this recently introduced metro infrastructure on urban heat islands. Utilizing a multi-modal approach, the research incorporates remote sensing data, Land Use and Land Cover (LULC) patterns, mobile transect surveys along a segment of the metro stretch, and in situ data logging at three locations. The study reveals a strong correlation between mean Land Surface Temperature (LST) values and landscape metrics. The introduction of the elevated metro line resulted in a noteworthy decrease of 4.26 °C in UHI patterns in the month of May. It was also found that the varying land-use along the metro also plays an impact on average Surface Urban Heat Island Intensity (SUHII). The three elevated corridors demonstrate reductions in SUHII by 2.3 °C, 1.4 °C, and 1.3 °C. Mobile transect surveys indicate that afternoons show an average UHI Intensity (UHII) of 4.7 °C and 4.6 °C for road and metro-road scenarios, with the metro line exhibiting a comparatively lower UHII of 2.8 °C. Data logging reveals that the Metro_Veg (metro-line with vegetation on either side) scenario exhibits a more pronounced UHI effect compared to Metro_Build (metro-line with buildings on either side). Metro_Veg records the highest air temperature at 45.90 °C, followed by Metro_Build and Road_Veg (road with vegetation on either side) at 43.70 °C and 39.70 °C, respectively. The elevated metro structure provides shade on roads, resulting in the lowest surface temperatures in the metro scenario. Overall, the findings suggest that metro line infrastructure holds potential for UHI mitigation. While extending metro lines across every road may not be feasible, the study advocates for shading above roads as a practical mitigative measure. Future research can explore various structures and materials, including dynamic solutions, for mitigating UHI effects along urban roads, contributing to sustainable urban development.