Special Issue 1, December 2009
Article Number: 05
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A study of the summertime urban heat island over Delhi
P. Pandey, D. Kumar, A. Prakash, K. Kumar, and V.K. Jain

Pages 27-34

Abstract—Day and night time thermal mapping of Delhi and its surrounding regions has been done with MODIS data at a spatial resolution of 5 km for the months of April, May and June, 2007, 2008 and 2009. A close examination of the daytime thermal data reveals that a hot region starts developing in the south and south-west of Delhi during the month of April every year. As the summer season reaches its peak in the months of May and June, this hot region further expands to the west and north-west of Delhi, producing heat wave like conditions in the region. In comparison, daytime surface temperatures in central parts of Delhi are found to be significantly lower by 4-5°C during summer. A completely reverse trend is obtained for the night-time surface temperatures with areas surrounding Delhi being approximately 4-7°C cooler than the central parts of Delhi. An examination of the distribution of Aerosol Optical Depth over Delhi and surrounding regions in the summer months indicates that aerosols present in the atmosphere over Delhi seem to be playing a significant role in the observed thermal contrasts over Delhi and the surrounding regions. Generally, AOD levels over Delhi are found to be significantly higher (0.7-1.1) than those over the surrounding regions (0.36-1.0). Further, it is observed that areas with high AOD levels generally tend to have lower surface temperatures during daytime whereas areas with low AOD levels tend to have higher surface temperatures.

Keywords—aerosol, AOD, surface temperature, UHI.