title: Flip flop of Day-night and Summer-Winter Surface Urban Heat Island Intensity in India.
abstract: The difference in land surface temperature (LST) between an urban region and its nearby non-urban region, known as surface urban heat island intensity (SUHII), is usually positive as reported in earlier studies. India has experienced unprecedented urbanization over recent decades with an urban population of 380 million. Here, we present the first study of the diurnal and seasonal characteristics of SUHII in India. We found negative SUHII over a majority of urban areas during daytime in pre-monsoon summer (MAM), contrary to the expected impacts of urbanization. This unexpected pattern is associated with low vegetation in non-urban regions during dry pre-monsoon summers, leading to reduced evapotranspiration (ET). During pre-monsoon summer nights, a positive SUHII occurs when urban impacts are prominent. Winter daytime SUHII becomes positive in Indo-Gangetic plain. We attribute such diurnal and seasonal behaviour of SUHII to the same of the differences in ET between urban and non-urban regions. Higher LST in non-urban regions during pre-monsoon summer days results in intensified heatwaves compared to heatwaves in cities, in contrast to presumptions made in the literature. These observations highlight the need for re-evaluation of SUHII in India for climate adaptation, heat stress mitigation, and analysis of urban micro-climates.
authors.affiliation: Interdisciplinary Program in Climate Studies, Indian Institute of Technology Bombay, Mumbai, 400 076, India.|C. S. Patel Institute of Technology, Charotar University of Science and Technology, Anand, 388421, India.
authors.forename: Hiteshri
authors.initials: H
authors.lastname: Shastri
authors.affiliation: Interdisciplinary Program in Climate Studies, Indian Institute of Technology Bombay, Mumbai, 400 076, India.|Department of Civil Engineering, Indian Institute of Technology Bombay, Mumbai, 400 076, India.
authors.forename: Beas
authors.initials: B
authors.lastname: Barik
authors.affiliation: Interdisciplinary Program in Climate Studies, Indian Institute of Technology Bombay, Mumbai, 400 076, India.|Department of Civil Engineering, Indian Institute of Technology Bombay, Mumbai, 400 076, India.
authors.forename: Subimal
authors.initials: S
authors.lastname: Ghosh
authors.affiliation: Interdisciplinary Program in Climate Studies, Indian Institute of Technology Bombay, Mumbai, 400 076, India.|Chemical Engineering, Indian Institute of Technology Bombay, Mumbai, 400 076, India.
authors.forename: Chandra
authors.initials: C
authors.lastname: Venkataraman
authors.affiliation: Interdisciplinary Program in Climate Studies, Indian Institute of Technology Bombay, Mumbai, 400 076, India.|Chemical Engineering, Indian Institute of Technology Bombay, Mumbai, 400 076, India.
authors.forename: Pankaj
authors.initials: P
authors.lastname: Sadavarte