Urban heat island effect of a polynuclear megacity Delhi - Compactness and thermal evaluation of four sub-cities

Planning for sustainable cities generally focuses on compact, human-scale cities. The urban paradigms underlying each city produce morphologies which generate a distinctive local urban climate. In this paper, four sub-cities in Delhi NCR, India, are classified using local climate zone (LCZ), and then analysed for thermal performance and compactness. These sub-cities are broadly classified as a garden city (LCZ 5(A)), a resettlement colony (LCZ 3), a mixed land-use city (LCZ 5), and an industrial city (LCZ 5(6)). The surface UHI (UHISurf) is estimated using Google Earth Engine with MODIS, canopy layer UHI (UHIUCL) with meteorological data, and density using Spacematrix. The nighttime UHIUCL is 7.52 degrees C (LCZ 5 and LCZ(A)) and the UHI(Surf )is 5.2 degrees C (LCZ 5 and LCZ D). A major apprehension is the residual temperature at sunrise (5-8 degrees C) leading to high heat stress and detrimental health impacts. The heating and cooling rate, reduced by a factor of three is observed (LCZ 5-0.25 degrees C/h). The least UHI is experienced by LCZ 5(A) and the built density is highest in LCZ 3. The mixed-land use (LCZ 5) city performs poorly, whereas the industrial city (LCZ 5(6)) performs optimally on both thermal and density scales.