Analysis for seattle, washington | 2020
In Seattle, our analysis found that urban heat islands increase maximum temperatures by as much as 6° F above the local baseline. Combined with regional climatic effects, neighborhoods in Central and South Seattle may be as much as 14° F hotter than neighborhoods in North Seattle. 33,000 people live in neighborhoods where maximum temperature exceed the 80th percentile and where average per capita incomes are less than 200% the federal poverty level (identified by black outline in the map below). 10,300 people live in areas that meet the above criteria, have a high percentage of population in high risk age groups (under age 14 or over age 65), and exceed 50% of regional population density. Every additional degree carry significant public health costs.
In the Seattle’s most severe urban heat islands, all-cause mortality rates are estimated to increase by as much as 7.7% when regional temperatures exceed 82°F. Seattle experiences 25 days above 82° per year, on average. Our model estimates that 8 – 15 lives are lost in the city each year due to extreme heat exacerbated by urban heat islands.
The public health burden of urban heat islands is disproportionately levied on the lowest income households (Table 1). In Seattle there is a strong correlation between household income and urban heat islands.
Without intervention, Seattle’s heat island impacts will grow significantly in a changing climate. Number of days above the 82° F threshold has increased by more than 50% since 1980 (Table 2). On the current trajectory Seattle will experience 42 days above the temperature threshold by 2050, and 59 days above the threshold by 2100.
“There is a strong correlation between summer heat and negative health outcomes. Temperatures above 82°F significantly increase the risk of cardiovascular diseases, respiratory illnesses, and heat stroke.”
*High Risk Area is defined as neighborhoods where the urban heat islands increase temperatures by 2°F or more and where average per capita incomes are less than 200% the federal poverty level.
**Highest Risk Area is defined as neighborhoods where High Risk Area criteria is met as well as a high percentage of population in high risk age groups (under age 14 or over age 65).
Wildish, J. 2020. Urban Heat Island Analysis: Seattle, Washington. Earth Economics. Tacoma, WA.
References
Anderson, B. G., & Bell, M. L. (2009). Weather-related mortality: how heat, cold, and heat waves affect mortality in the United States. Epidemiology (Cambridge, Mass.), 20(2), 205.
Department of Environmental Health, Harvard T.H. Chan School of Public Health. 2016. Study on the Association Between Ambient Temperature and Mortality Using Spatially Resolved Exposure Data. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5071163/
Wang, Y., Akbari, H., 2016. The Effects of Street Tree Planting on Urban Heat Island Mitigation in Montreal. https://doi.org/10.1016/j.scs.2016.04.013.