Surface urban heat island effect of a polynuclei megacity Delhi – morphological and thermal evaluation of three sub-cities

Urbanization is bound to have climatic ramifications due to its interference with the energy balance. Urban heat island effect is one such inevitable consequence, causing the most urbanized area of the city to be warmer than surroundings. A megacity such as Delhi has several heat islands, as it’s an amalgamation of several cities. It comprises of cities built in different centuries and based on unique urban planning concepts. Urban form and function essentially characterise's the climate of the city. A sustainable urban city has to strike balance between its morphometric and climatic performance. Prioritisation of one over other gives either gives thermally efficient cities with low socio-economic gains or otherwise. Thus, testing the new notion of dense cities with mix-land use on the thermal climatic scale is of prime importance.

Delhi has been the seat of power for more than 650 years, thus many dynasties built their capitals. It is one of the most populated megacity but only from the last two decades. Due to it's geological location, it faces heat waves each year. Three sub-cities have been selected to analyse the surface urban heat island and socio-economic performance. The oldest city is Shahjahanabad built in 1640s with organic urban form on the banks of Yamuna river with highest population density in Delhi. Second is Lutyen’s Delhi, built in 1930’s as a result of garden city movement under the influence of British architecture. It has geometrical designs and seventy times less population than old delhi. A new city Gurgaon has been selected, built in 1990s to decongest the population load of core Delhi. It was built according to mix land use concept and has twenty times more population than Lutyen's Delhi. The principles governing the development in the sub-cities are unique, thus it’s interesting to compare them to identify which planning pattern performs best.

Surface UHI Intensity is estimated using Landsat 8 data for 2015 in the local climate zones of the sub-cities. The Land surface temperature has been corrected for atmospheric and emissivity errors. Morphometric matrix such as mixed used index and space syntax have been computed for estimating the socio- economic connectivity . Intuitive hypothesis was that Gurgaon should perform best in aggregation of morphometric and thermal scores, as it emphasises on implementing new urbanism. In complete astonishment, oldest city Shahjahanabad has performed way better than the most planned city Gurgaon. Further, heat fluxes have been modelled using Surface Urban Energy and Water Balance Scheme at a simple level using Urban Multi-scale Environmental Predictor. Parameters have been manually by field work estimation. The negligible anthropogenic heat flux and organic mix land use pattern of Shahjahanabad explain the results obtained. It questions if our new urban cities are built to create heat islands? or may be new urbanism ideas are well implemented in old cities of Delhi.