About 80% of the U.S. population lives in cities, where the urban heat island effect can worsen heat extremes. Climate Central analyzed how urban heat island intensity varies within 44 major U.S. cities that together account for nearly one-quarter of the total U.S. population. This analysis calculates the urban heat island (UHI) index for each census tract within a city to estimate how much hotter these areas are due to the characteristics of the built environment. Maps show urban heat hot spots within each city—whether concentrated in the urban core (e.g., Indianapolis) or sprawling across a vast developed area (e.g., Detroit). Across all 44 cities, the total population living in census tracts with an UHI index of 8°F or higher is 41 million—or about 55% of the 74 million people included in this analysis. Nine cities had at least 1 million people exposed to an UHI index of 8°F or higher—meaning that people in those census tracts feel at least 8°F more heat because of the local built environment. The average UHI index per capita was lowest in Wichita (7.2°F) and highest in New York (9.5°F), San Francisco (8.8°F), Chicago and Miami (8.3°F), and Seattle (8.2°F). The average UHI index by area ranged from 5.8°F in Las Vegas to 8.6°F in New York. Planting street trees and installing cool roofs and pavements are among the ways to reduce local heat islands.

Daniel J. Vecellio (Virginia Climate Center, George Mason University)