Spatio-Temporal Variations and Effect of COVID-19 Led Lockdown on Urban Heat Island (UHI) and Urban Pollution Island (UPI) Over Delhi Region During 2017–2021

The urban environment is at substantial risk due to the pace of urbanization. There are two major components of the urban environment viz. urban heating and urban pollution . The outbreak of the COVID-19 pandemic and the associated lockdown provided a stability to the deteriorating environment and all associated parameters. The study focuses on understanding the changes in the surface urban heat island (SUHI) and atmospheric/near-surface urban pollution island phenomenon (AUPI/NSUPI) as a result of lockdown in 2020 and 2021 w.r.t. averaged values of 2017–19, through parameters like LST, AOD, NO 2 and PM 2.5 for the Delhi region (Delhi urban area or DUA and non-urban area surrounding DUA) using in situ and remote sensing satellite measurements. A remarkable reduction in mean daytime/nighttime LST (1.99 °C/1.80 °C) using MODIS datasets and 5.46 °C using Landsat datasets was observed in LD-1 of 2020. SUHII values were 0.35 °C higher in 2020 as compared to 2017–19 due to thriving vegetation. Similarly, annual NO 2 /PM 2.5 reduced by 61.39%/11.78% and satellite-based NO 2 /AOD reduced by 28.87%/9% in 2020 compared to 2017–19. A yearly reduction of ~ 41%, ~ 6%, ~ 10% and ~ 39% was observed in NSUPII (NO 2 ), NSUPII (PM 2.5 ), AUPII (AOD) and AUPII (NO 2 ), respectively. The environmental regime of the urban purlieu was revitalized, and the ecological sensitiveness was restored by vegetation growth and reduced anthropogenic activities; however, the scenario was quickly restored in 2021 showing increased pollution levels.