New York City, like other large cities, is warmer than surrounding areas due to the urban heat island effect, which occurs when impervious built surfaces such as roads and buildings absorb solar radiation and re-radiate it in the form of heat. Spatial and temporal variation in surface and near-surface air temperature in New York City can best be described as an "urban heat island archipelago." Mitigation strategies such as urban forestry, living (i.e., green, vegetated) roofs, and light-colored surfaces can be implemented at the community level. However, understanding how these strategies interact with the urban environment requires a combination of input from stakeholders, regional climate modeling, satellite and GIS data, street-level reconnaissance, and cost-benefit analysis.

The development of a heat island has regional-scale impacts on energy demand, air quality, and public health. Use of fossil fuels to satisfy the increased energy demand contributes to emissions of greenhouse gases that in turn cause global climate change; global climate change is likely to exacerbate urban heat islands, making cities even hotter. Although the heat island effect occurs throughout the year, its occurrence during the summer months is of particular public policy concern because of the association of higher temperatures with increases in electric demand due to air conditioning, elevated air pollution and heat-stress related mortality and illness. The choice of mitigation strategy ultimately depends on the environmental and social priorities of stakeholders, as well as on the existing configuration of a neighborhood and other physical constraints.

RESEARCH OBJECTIVES

1. Analyze and model the heat island effect in New York City;
2. Test urban forestry, living roofs, and light surfaces as potential heat island mitigation strategies city-wide and in six case study areas;
3. Improve scientific understanding of how urban heat island mitigation strategies affect New York City's surface and near-surface air temperatures;
4. Evaluate potential interactive consequences associated with heat island mitigation strategies with particular attention to land use, electric loads, and potential air quality and/or health impacts;
5. Test the impact of temperature reduction on energy demand; and
6. Determine the cost-effectiveness of each strategy.

This research is a collaboration between researchers at the Columbia University Center for Climate Systems Research and Hunter College - City University of New York. The principal investigators are Cynthia Rosenzweig and William D. Solecki.

One project, Mitigating New York City's Heat Island with Urban Forestry, Living Roofs, and Light Surfaces, was sponsored by the New York State Energy Research and Development Authority (NYSERDA) and the New York State Department of Environmental Conservation. The Research Report is available in pdf format from NYSERDA.

The citation for this report is:

Rosenzweig, C., W.D. Solecki, and R. Slosberg. 2006. Mitigating New York City's Heat Island with Urban Forestry, Living Roofs, and Light Surfaces. A report to the New York State Energy Research and Development Authority. 123 pages.