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.
Sci Rep. 2017 Jan 9;7:40178. doi: 10.1038/srep40178.
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.
城市区域与其附近非城市区域之间的地表温度差异（LST），即表面城市热岛强度（SUHII），通常为正值，这在早期研究中已有报道。印度在过去几十年经历了前所未有的城市化进程，城市人口达到 3.8 亿。在这里，我们首次研究了印度 SUHII 的日变化和季节变化特征。我们发现，在季风前夏季（MAM）的白天，大部分城市地区的 SUHII 呈负值，与城市化的预期影响相反。这种出乎意料的模式与季风前夏季干旱时非城市地区植被较少有关，导致蒸散（ET）减少。在季风前夏季的夜间，当城市影响显著时，会出现正的 SUHII。冬季白天，在印度恒河平原，SUHII 也会呈现正值。我们将 SUHII 的这种日变化和季节变化归因于城市和非城市地区 ET 差异的相同原因。季风前夏季白天，非城市地区的 LST 较高，与文献中的假设相反，这导致与城市热浪相比，热浪更加剧烈。这些观测结果强调了需要重新评估印度的 SUHII，以适应气候变化、减轻热应激以及分析城市微气候。
