The narrow island of Manhattan, located between the Hudson River and the East River, is a familiar feature to crews on the International Space Station. The ragged line of shadow cast by the Palisades cliff (in New Jersey) crosses the bottom of the image. Wharves jut into the rivers; bridges are visible thanks to the shadows they cast; and the grid pattern of major streets stands out. On Manhattan itself, the main visual features are Central Park (with playing fields appearing as white dots) and two darker zones where the tallest buildings of Midtown and the Financial District cast long shadows even in this early afternoon view.
In such an urban setting, rivers and parks can reduce the heat island effect, the local zone of higher surface and air temperatures caused by the way concrete and tarmac (asphalt) absorb, store, and release heat. Rivers provide pathways for wind, and the cooling effect of vegetated parks can be detected by space-based instruments that measure the temperature of the ground surface.
Tall buildings have a more complex effect. Shadowed zones in the “urban canyons” between tall buildings receive fewer hours of direct sunlight per day. But where that light can reach the canyon floors, energy is reflected back up at the walls of the buildings, where it is absorbed and later released as heat. This is especially the case at night, when urban canyons retain more heat than parts of the city with shorter buildings.
- Environmental Protection Agency Reducing Urban Heat Islands: Compendium of Strategies Urban Heat Island Basics. Accessed June 6, 2014.