High air temperatures are a public health threat, causing 1300 deaths annually in the United States (US) along with heat-related morbidity and increased electricity consumption for air-conditioning (AC). Increasing tree canopy cover has been proposed as one way to reduce urban air temperatures. Here, we assemble tree cover and developed land-cover information for 97 US cities, housing 59 million people, and use regression relationships to analyze how much current urban tree cover reduces summer (JJA) air temperatures and associated heat-related mortality, morbidity, and electricity consumption. We find that 78% of urban dwellers are in neighborhoods with less than 20% tree cover. Some 15.0 million people (25% of total) experience a reduction of 0.5–1.0°C from tree cover, with another 7.9 million (13% of total) experiencing a reduction of greater than 1.0°C. Current relationships between temperature and health outcomes imply that urban tree cover helps avoid 245–346 deaths annually. Heat–mortality relationships in the 1980s, when a smaller fraction of US households had AC, imply a greater role in the past for urban tree cover in avoiding heat-related mortality. As AC availability has increased, the value of tree cover for avoiding heat-related mortality has decreased, while the value of tree cover for reducing electricity consumption likely has increased. Currently, for the 97 cities studied, the total annual economic value of avoided mortality, morbidity, and electricity consumption is an estimated $1.3–2.9 billion, or $21–49 annually per capita. Applying our results to the entire US urban population, we estimate urban tree cover annually supplies heat-reduction services worth $5.3–12.1 billion.
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The authors thank their institutions for research support during the writing of this paper. RIM and TK were supported by a grant from the China Global Conservation Fund. PH thanks the Marianne and Marcus Wallenberg Foundation for their financial support. We also thank those who created the datasets used in this paper, including the NLCD, WUI, and the Global Historical Climatology Network. Without their data, our analysis would not have been possible.
The group jointly designed the research. RIM coordinated data analysis and wrote the paper with the help of the other coauthors. PZ assembled the information on air temperature and land cover, while PH worked on the methodology for estimating heat-related impacts. TK led the economic valuation analysis.
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The strength of the statistical relationship between urban tree cover and temperature, as a function of spatial scale. Shown on the Y-axis is the T-value of the parameter, with greater absolute values (farther from zero on the y-axis) having greater explanatory power. We display the trend for maximum summer daily temperature (red), minimum summer daily temperature (blue), and mean summer daily temperature (black) (TIFF 20 kb)
The strength of the statistical relationship between developed cover and temperature, as a function of spatial scale. Shown on the Y-axis is the T-value of the parameter, with greater values having greater explanatory power. We display the trend for maximum summer daily temperature (red), minimum summer daily temperature (blue), and summer daily mean temperature (black) (TIFF 20 kb)
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McDonald, R.I., Kroeger, T., Zhang, P. et al. The Value of US Urban Tree Cover for Reducing Heat-Related Health Impacts and Electricity Consumption. Ecosystems 23, 137–150 (2020). https://doi.org/10.1007/s10021-019-00395-5
- air temperature
- energy use
- heat waves
- United States