Impacts of increased urbanization on surface temperature, vegetation, and aerosols over Bengaluru, India

Bengaluru is India's third largest city by population and has been noted as a prime example of rapid urbanization due to the increased presence of the information technology industry. Urban areas are typically characterized by (1) higher land surface temperatures (LST) when compared to their surroundings, known as the urban heat island (UHI) effect, and (2) lower vegetation spatial extent and density. However, an observational study exploring the impacts of increased urbanization on surface temperature and vegetation in Bengaluru during different seasons and time of day is lacking. Here, satellite products of LST, Enhanced Vegetation Index (EVI), aerosol optical depth, and land cover from the MODerate Resolution Imaging Spectroradiometer (MODIS) were used to assess changes in EVI and daytime and nighttime LST over Bengaluru and surrounding non-urban areas from 2003 to 2018 for the dry (December-February) and wet (August-October) seasons. Results showed that the amount of urbanized land increased by 15% from 2003 to 2018. The mean UHI intensity was found to be of greatest magnitude during the dry season at nighttime, and an UHI was also observed for the wet season during both daytime and nighttime hours. The UHI intensity exhibited an increasing trend in the dry season nighttime and wet season daytime and nighttime, suggesting an enhanced UHI effect with increased urban area. Results further show an absence of a daytime UHI during the dry season with a significant daytime cooling trend most likely attributable to an increase in aerosols, which act to limit daytime surface warming. Understanding the relationships among urbanization, UHI intensity, vegetation, and aerosols, and how they change with time could be useful to project future UHI impacts in Bengaluru.