Summer in the City
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Hi, I'm Dave Thurlow for the Weather Notebook. New research suggests that ur-ban heat islands are becoming larger and causing climate changes. Metropolitan areas soak up heat all day in asphalt, concrete, and buildings. For example, 95-degree days can cook rooftops to temperatures higher than 170 degrees. Scientists call these areas urban heat islands.

These islands are creating strange weather patterns. Cities release stored heat when the sun sets, creating a column of low pressure. It's like a chimney that sucks in cooler air. This creates winds. Then the dome of heated air forms convective clouds that bring rain and thunderstorms. Scientists are convinced the storms are manmade because they occur at very strange times, for example, at two in the morning.

Urban heat islands represent an increasing number of cities with stifling, unhealthy air. A predicted 80 percent of the world's population will live in cities by 2025; making urban heat islands quite a cause for concern. In rural areas, the solar energy absorbed near the ground evaporates water from the vegetation and soil. A major factor of urban heat islands is that developers cut down trees to build suburbs. Trees provide shade from the heat and absorb the sun's harmful rays. Without them, the effect is like an urban desert.

Researchers hope that state and local governments will use their findings as a springboard to adopt "cool community measures." These alternatives include planting trees and using roofing materials that can reflect 60-80 percent of incoming sunlight.

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