Assessing urban drivers of canopy layer urban heat island: A numerical modeling approach

Abstract

The physical and geometrical properties of urban regions are responsible for influencing canopy layer air temperature leading to urban heat island effect (UHI). Local climate zone (LCZ) land cover classification scheme has been widely adopted to examine UHI and inter urban heat island (IUHI). In tropical cities with heterogeneous mix of urban surface cover, morphology, thermal and radiative properties pose the question–which built properties have a higher influence on UHI? This study evaluates UHI response in tropical city Nagpur (India) using LCZ and city specific built parameters. It uses mobile survey to collect nocturnal air-temperature data during two consecutive summers (2016 and 2017). The study identifies eleven built environment parameters from literature survey. It adopts a unique approach of all possible regression technique with series of checks and model validation (coefficient signage, variance inflation factor, p-value & t-statistics, R square, F value and k-fold cross validation). The result shows distance from central business district (DI), surface albedo (AL), aspect ratio (AR) and vegetation density ratio (VDR) as major predictors explaining UHI response. Every 500 m increase in DI reduces inter urban heat island (IUHI) by 0.13 °C. Increasing AL by 0.01 decreases UHI by 0.18 °C whereas increasing VDR by 0.10 yields 0.17 °C reduction in IUHI. 10% increase in AR suggests IUHI increase by 0.17 °C. This study contributes in exploring mitigation strategies for complex built environment. It enables urban planners, designers and policy makers to approach urban intervention with scientific and sustainable approach.