The Response of the Urban Heat Island to El Niño-Southern Oscillation

Abstract

Currently about half of the world’s population resides in cities, which tend to be warmer than surrounding rural areas. This phenomenon is referred to as the Urban Heat Island (UHI). The UHI has important implications for health and mortality. El Niño-Southern Oscillation (ENSO), which describes the periodic variation in sea surface temperatures over the equatorial Pacific Ocean, has been found to contribute to UHI variability. However, there are very few studies in the literature that examine the relationship between the UHI and ENSO. Those that exist do not account for urban climate feedbacks and limit their scope to the city-scale. We use a coupled climate model with an urban component to develop a more comprehensive study of present day UHI responses to ENSO on a larger regional scale. We focus on South Asia, a region which experiences ENSO teleconnections and contains a large portion of the global urban population. We investigate how the response of UHI to ENSO differs across different climate regimes and seasons within the region. We find that there is an urban cool island during both pre-monsoon summer and the monsoon season in the mean state. El Niño intensifies this mean state trend in humid regions and opposes it in arid regions. Inversely, La Niña intensifies the mean state in arid nighttime and opposes it in humid daytime.