Mitigating New York City's Heat Island with Urban Forestry, Living Roofs, and Light Surfaces

New York City, like other large cities, is warmer than surrounding areas due to the urban heat island effect caused by absorption of heat by building materials and lack of vegetation. Heat island mitigation strategies, such as urban forestry, living/green roofs, and light surfaces, could be implemented at the community level within New York City, but their effects have not been tested with a comparable methodology. Using a combination of simple and complex regional climate models (e.g. MM5), this study evaluates whether these three strategies can reduce surface temperatures as well as near-surface air temperatures enough to have a measurable impact on the heat island, especially at peak times on hot summer days. The study further considers which strategy or combination of strategies is optimal given prevailing meteorological conditions and current patterns of land use and land cover in the city.

Results showed that land cover plays a dominant role in determining heat island potential in New York City. Using the project methods, we found that that the relationship between vegetation and surface temperature is stronger than the relationship between urban geometry – e.g. building heights, road density – and surface temperature. Vegetation was found to have a greater effect on surface temperature than albedo.

Since vegetation has a significant effect on surface temperature, the redevelopment of urban surfaces to increase vegetation cover could significantly reduce New York City's surface temperature. Surface temperatures are related to air temperatures, and thus land cover modification could also affect the city's air temperature.

The cooling effect of trees on surface temperature tends to be localized rather than spread to adjacent areas. Remotely-sensed surface data show that the cooling effect of trees tends to be limited to 200 feet (61 meters).