The Sunny Side of the Street

If Manhattanhenge, discussed in my prior blog, broadcasts the relationship between Manhattan’s street grid and the sun’s seasonal path, summer’s heat pushes us to respond to the sun’s path with innate astronomical awareness in our daily lives.

With summer in full blast, the sun’s heat radiates off sidewalks and buildings and intensifies the temperature. As a walker in Manhattan, whether for pleasure, errand running, or as part of my daily commute, I often assess what side of a street is better shaded, and choose that side for my walk. With the longer stretches of my walk extending in a north-south/south-north direction, this means walking on the east side of an avenue in the morning and the west side in the evening. The difference in temperature is significant. Winter brings the opposite effect: seeing out the sunnier side of the street for greater warmth and light.

Orientation to the sun has figured in town and city planning for centuries, typically as a way to enhance warmth and light long before the development of modern heating and lighting systems. Notably, in 1916 New York City passes a zoning resolution to preserve sunlight at street level, recognizing sunlight as a public good. At the time, buildings were limited in height—and sun-blocking effects—by engineering capabilities.

With continual improvements in elevators and the use of steel frame structures, building height have multiplied, impacting street-level sunlight. At the same time, urban landscape materials—asphalt, metal, and dark buildings—absorb more sunlight than forests, fields, and snow-covered terrain, resulting in an “urban heat island”, were a city’s temperature is significantly warmer than in surrounding areas. New York City’s heat island effect is most felt at night, when the temperature is 5 to 7 degrees warmer than in surrounding areas.

Scientists and urban planners have considered how attention to the interplay of urban structures and sunlight can enhance energy conservation by cooling the city. NASA determined that dark, sunlight absorbing black roofs in New York City reached 170 degrees on July 22, 2011, a peak day in a heat wave that resulted in a city record for electricity usage. By contrast, white roofs were 42 degrees cooler. This led to the widespread installation of white roofs, with the aim of decreasing electricity usage and reducing city temperatures.

While not as extreme as the impact of roof-top lightening, a shift from the sunny to the shaded side of a city street in the middle of Julycan offer a welcomed refuge. If you find yourself wandering down a city street during the heat of summer, think about how you intuitively position yourself for cooling comfort. We’re not so different from other animals in this way!

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