Characteristics of Remotely Sensed Urban Pollution Island (UPI) & its Linkage with Surface Urban Heat Island (SUHI) over Eastern India

The urbanisation and its detrimental impact on climate is a well-documented phenomenon in today’s world, but research documenting the Urban Pollution Island (UPI) especially over South Asia is seldom found. With the advancement of the satellite datasets, the quantification of UPI has become possible only in recent years. When measured using satellite data, the UPI is the spatial anomaly of Aerosol Optical Depth (AOD) over an urban area with reference to a nearby non-urban zone. UPI may influence energy budget, precipitation patterns and human health over the city. In the present research, it has been attempted to analyse the climatology and characteristics of UPI and its association with the Surface Urban Heat Island (SUHI) over six cities (Patna, Gaya, Ranchi, Jamshedpur, Bardhaman and Siliguri) from eastern India, which is a highly populated region and infamous for climatic concerns. Alongside, a Surface PM2.5 data is also investigated further, to find heat and pollution island links. The UPI–SUHI interactions have been evaluated and found to be very distinct for each city. It is found that high urban AOD value can be noticed irrespective of the UPI magnitude over Patna. Bardhaman has exhibited very high AOD (> 3.0) even in very low UPI conditions. Jamshedpur’s urban loadings found to be contributing somewhere to UPI formations. UPII has also shown a clear sign of a seasonal cycle across the cities. In Patna, increase in PM2.5 may be linked to SUHII in medium loading cases and very high PM2.5 loadings (> 200 μg/m³) result in low average SUHII. It may be summarised that Patna, Gaya and Bardhaman are exhibiting high surface PM2.5 loads over urban zones, whilst Ranchi, Siliguri and Jamshedpur have much cleaner urban air. The Mann–Kendall test and Pettitt’s test also detected significant increasing trend and change point in recent times for UPI intensity. The well-developed UPI system shows an exigency of more in-depth studies to mitigate the detrimental effects of UPI–SUHI in upcoming times.