An energy and mortality impact assessment of the urban heat island in the US

• The urban heat island (UHI) may actually be beneficial in colder cities in the US in terms of energy use
• The UHI may cause an increase in heat related mortality of ~ 1 deaths per million
• In winter the UHI may decrease cold related mortality by ~ 4 deaths per million
• Cold related death rates were 3 times higher in rural areas although the homeless population live mainly in urban areas

Increased summer energy use and increased summer heat related mortality are the two most cited detrimental impacts of the urban heat island (UHI). An assessment of these impacts was made that considered the annual impact of the UHI, not just the summer impact. It was found that in north of the US there was a net decrease in energy use from the UHI, as heating energy reductions were larger than the increase in cooling energy. In the south there was a net energy increase from the UHI. The impact of the UHI on heat related deaths was an estimated increase of 1.1 deaths per million people. The impact of the UHI on cold related deaths was an estimated decrease of 4.0 deaths per million people. These estimates are caveated by the acknowledgement that compounding factors influence mortality. Hypothermia related death rates were three times higher in rural areas than urban areas. This is surprising as the homeless population is usually considered the most at risk, yet they mostly live in urban areas.