Fact of the Day

People here often stare at me like I’m crazy when I say that motor vehicles here a large contributor to the hotness of Singapore’s environment (largely because they demand so much tarred space, and tar is a major contributor to the Urban Heat Island Effect). This excerpt from a Science review of urban ecology, therefore, may be of interest:

The best-documented example of anthropogenic climate modification is the urban heat island (UHI) effect: Cities tend to have higher air and surface temperatures than their rural surroundings, especially at night. Several characteristics of urban environments alter energy-budget parameters and can affect the formation of the UHI. These include land-cover pattern, city size (usually related to urban population size), increased impervious surfaces (low albedo, high heat capacity), reduced areas covered by vegetation and water (reduced heat loss due to evaporative cooling), increased surface areas for absorbing solar energy due to multistory buildings, and canyon-like heat-trapping morphology of high-rises. The UHI is a local phenomenon with negligible effect on global climate, but its magnitude and effects may represent harbingers of future climates, as already-observed temperature increases within cities exceed the predicted rise in global temperature for the next several decades. Kalnay and Cai estimated that urbanization and other land-use changes accounted for half of the observed reduction in diurnal temperature range and an increase in mean air temperature of 0.27°C in the continental United States during the past century. By comparison, downtown temperatures for the United States have increased by 0.14° to 1.1°C per decade since the 1950s. Research on the effects of elevated temperature on remnant ecosystems (e.g., parks and open space) within cities, particularly when other variables are controlled, may contribute much to our ability to predict how ecosystems will respond to global climate change.

UHI affects not only local and regional climate, but also water resources, air quality, human health, and biodiversity and ecosystem functioning. Urban warming in hot climates exerts heat stress on organisms, including humans, and may influence water resources by changing the surface-energy balance, altering not only heat fluxes but also moisture fluxes near the surface. UHI may induce the formation of photochemical smog and create local air-circulation patterns that promote dispersion of pollutants away from the city. In warm regions (and summertime of cooler regions), urban warming greatly increases energy consumption for cooling. For example, about 3 to 8% of electricity demand in the United States was estimated to be used to compensate for UHI effects, representing another indirect feedback to global climate change. One way to mitigate the UHI effect is by increasing vegetation cover and albedo, but this strategy is a trade-off requiring greater water use, especially in arid regions.

The emphasis is mine. Since Singapore’s average temperatures are much higher than the average city temperature in the US, I imagine that the proportion of Singapore’s electricity demand used to compensate for UHI would be at least on the high end of 3-8%.

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