Researchers from the University at Albany, State University of New York, funded in part by CPO’s Climate Observation and Monitoring (COM) program, have recently published a study that demonstrates multiple methods for identifying the major factors controlling urban heat in a city. While the study takes Bengaluru, India, as an example, the methods used are applicable to any urban city.
Published in Urban Climate, the study focuses on Bengaluru, the third most populous city in India and a textbook example of a rapidly urbanized city. Using a variety of statistical methods, the authors determined that vegetation, or the lack thereof, was the leading factor influencing the intensity of urban heat during both the wet and dry seasons in Bengaluru.
Urban heat is where cities are warmer than their surrounding rural areas, thus increasing the risk of heat- and respiratory-related illness for a city’s inhabitants. There are many factors that influence urban heat and they can differ by city. Properly quantifying the relationship between these factors helps policy makers determine appropriate mitigation strategies.
For Bengaluru, vegetation was the main factor controlling urban heat during the day for both the wet and dry seasons. Areas with fewer plants had limited evaporative cooling compared to areas with more. However, specific humidity was the leading factor at night during the wet season, as increased water vapor enhances the heat emitted back towards Earth from the atmosphere and warms the city surface. Given that vegetation and specific humidity are interrelated, the study authors suggest that any mitigation strategies which increase vegetation in Bengaluru should not substantially increase water vapor, otherwise urban heat may also increase at night during the wet season.