Urban Heat Island Effect

Urban sprawl used to be contentious because of the loss of greenspace around cities, erosion of farmland, increased commuting time, big box stores located out of town, and a whole bunch of other social related items. But, cities also generate, absorb and store a lot of heat energy and that could be a big problem for city-dwellers.

We all know cities can get really hot, sticky, and sweaty in the summer too, but just how hot do they get and what does that do for the environment and health of its people?

The urban heat island is a phenomenon where solar power absorbing plants (trees, grass, soil, lakes, etc.) are replaced by high thermal inertia concrete, asphalt and highly reflective glass (which causes multiple sun reflections), combined with an impermeable surface where not even water can trickle into the ground, making for ideal conditions for generating local hot spots.

For example, NASA’s Landsat 7 satellite mapped Buffalo, New York, on August 3, 2002 using an Enhanced Thematic Mapper instrument that measured temperature (see image below). The results showed temperature variations ranging from red (warm) to yellow/white (hot). As 46% of Buffalo is densely developed, some parts of the city have surface temperatures 7.2°C (almost 13F) warmer than its surroundings, which contrasts with the surrounding farmland in the image.

During heat waves, cities can get stifling and dangerously hot, when people generally do not drink enough water to stay hydrated or do not have air conditioning to take the sting out of the heat, and at least get some restful night-time sleep. Increased air conditioning use can also put a major strain on the electrical grid, which may also be suffering the effects of high temperatures on its transformers and power lines.

Extremes of heat can also lead to increased deaths amongst the old, young and infirm. Over 15,000 people died in Paris during a 2003 heat wave, and perhaps as many as 70,000 across Europe. So the effects of city heat, combined with heat waves, should not be taken lightly.

So why not take some of the heat out of the city, without adding lots of air conditioning that just ends up requiring more power stations (and more greenhouse gases and more global warming with yet more global climate extremes). Paint roofs white instead of black, install green roofs where possible, and even use white concrete instead of black tarmac for rebuilt roads. Ditch the car; use urban transport, cycle or walk.

A striking image (above), taken by a NASA Lear Jet which measured the May 11-12, 1997, thermal data of metropolitan Atlanta, Georgia when normal daytime air temperatures of about 26.7°C (80F) contrast against city surface temperatures of 47.8°C (118F). Blue colors are cooler; red is hotter and extremely hot is white. It looks surreal.

According to Stuart Gaffin, an associate research scientist with the Earth Institute at Columbia University who studies urban heat islands, “About half the world’s population (3 billion people) now lives in cities. In a couple of decades, it’s going to be 5 billion people.”

That means bigger cities, higher urban temperatures, more demand for everything – including air conditioning, water and medical care, and bigger and more, urban heat islands. Gaffin’s research for the U.S. Global Change Research Program, predicts an increase of 30 or more days of heat waves with temperatures upwards of 90 degrees in New York over the few decades versus around 14 days of heat waves at present.

It seems that the old adage - "if you can’t take the heat, stay out of the fire" may need to be adjusted to "if you can't take the heat, stay out of the city".

Via NASA Urban Heat Islands & NASA Beating the Heat

Trevor Williams is a University of Victoria Mechanical Engineering PhD candidate specializing in renewable energy, power grid modeling and plug-in hybrid electric vehicles. He has a bachelors in Aeronautical Engineering, a Masters in Management Science and over 23 years international experience in the space industry, having worked on Earth observation and telecommunications satellites. He is the author of the Eco-Geek blog.

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