Inter-seasonal characterization and correlation of Surface Urban Heat Island (SUHI) and Canopy Urban Heat Island (CUHI) in the urbanized environment of Delhi

Abstract

The Intergovernmental Panel on Climate Change's (IPCC) 6th assessment report warns India about excessive heat. As India's population, urbanization, built-up regions, and concrete expand, vulnerable people may face higher heat risks. Delhi, India's capital and second-largest city, is noted for its excessive heat and air pollution. Heat in Delhi is spatially distributed and varies in magnitude due to built-up area density, the absence of a natural landscape, and other geographical aspects. To pinpoint the hotspot region, the study attempts to characterize Surface Urban Heat Islands (SUHIs) and Canopy Urban Heat Islands (CUHIs). Temporal and seasonal assessment of LST (Land Surface Temperature) using MODIS (Moderate Resolution Imaging Spectroradiometers) data and Ambient Temperature (AT) data from 39 Central Pollution Control Board (CPCB) monitoring stations with a representative radius of 1–5 km used to explore the inter-seasonal variation of SUHI and CUHI over the city in terms of magnitude and extent for 2019, 2020, and 2021. To describe SUHI and CUHI, a two-dimensional Gaussian fitting-based image analysis method is developed. The results show that the region's greatest SUHI magnitude is 2.36 °C in the monsoon season and 2.09 °C in the spring season. In comparison, the maximum CUHI magnitude is 4.74 °C and 3.15 °C in the Autumn and Winter seasons, respectively. The impact of SUHI can be experienced up to 82 km2 from the critical location in Winter and CUHI has 67.83 km2 in Summer. Inter seasonal comparison matrix between SUHI and CUHI demonstrates a positive but modest association due to considerable seasonal parameter fluctuation. UHI hotspot zone is at the centre of the urban with little seasonal fluctuation. South-West (SW) is a hotspot for SUHI and CUHI during the monsoon and spring seasons due to its dense residential and industrial areas. During winter, SUHI indicates SW as the critical zone and CUHI depicts NW. The finding shows that Delhi has a longer duration of hot weather. This study could help to understand UHI in Delhi at the local scale. The study shows UHI's seasonality and potential drivers. Critical hotspots and seasonal shifts should be used in urban development to improve Delhi's thermal environment.