Environmental impacts of COVID-19 lockdown on Indian metropolitan cities: a comprehensive analysis of air quality, water quality, and surface temperatures

The COVID-19 pandemic had a big influence on human civilization, and it also had an impact on the environment. The lockdown, which limited human activity, resulted in considerable environmental gains, particularly in terms of the purity of the air and water. This research examines the effects of the COVID-19 lockdown on surface water quality, land surface temperatures, and air quality in Indian Metropolitan Cities such as Ahmedabad, Kolkata & Howrah, and Hyderabad. Water quality is assessed based on the concentrations of suspended particulate matter (SPM). Land surface temperatures (LST) are calculated using Landsat 8 data. Air pollution levels, specifically NO₂, PM_2.5, and PM₁₀, are analyzed using data from the Central Pollution Control Board for the Maninagar, Ghusuri, and Bollaram Industrial Area stations in Ahmedabad, Howrah, and Hyderabad. The study observed a reduction in waterway turbidity during the lockdown. The analysis of SPM concentrations showed that SPM values during the lockdown period were 15% to 35% lower in the Sabarmati River and 5% to 25% lower in the Hooghly River compared to the pre-lockdown era. The lockdowns also led to improved air quality and reduced LST, which decreased the Urban Heat Island (UHI) effect in all metropolitan areas except Kolkata, where LST increased by 4 °C from 2019 to 2020. The concentration of NO₂ decreased by 68%. PM_2.5 levels were reduced by 8% to 72.37%, and PM₁₀ levels showed the most significant decrease, ranging from 5 to 72.09%. The study concludes that the lockdown measures implemented to curb the spread of the pandemic had a substantial impact on the environment, resulting in improvements in air quality, water quality, and surface temperatures. These findings emphasize the potential for substantial environmental improvements through mitigation measures and highlight the importance of integrating sustainable practices into urban planning and policy-making to achieve long-term environmental benefits.