Using the Heat Vulnerability Index

By Manny Srulowitz

Heating Up

New York is getting warmer. The annual statewide average temperature in New York has warmed 3°F (0.6°F per decade) since 1970, and average temperatures are projected to rise by as much as another 3°F by 2080. In addition to rising average temperatures, New York has seen an increase in extreme weather events, including the amount and length of heat waves. Periods of extreme heat have a profound effect on human health, including dehydration, heat exhaustion, heat stroke, and mortality. In New York City, specifically, extreme heat is the number one cause of mortality from extreme weather. In this past August alone, New York City endured more 90-degree days (11) than any August in over a decade, including a four-day heatwave. This summer, 725 New Yorkers visited the ER, nearly 13% more than during the same period last summer and almost as many as in 2018, according to data from the city Department of Health and Mental Hygiene. According to the New York City Heat-Related Mortality Report, each summer an estimated 370 New Yorkers die prematurely because of hot weather in New York City. These heat-related deaths account for about 2% of all deaths over the warm season months of May - September.

Credit: EPA

This problem is made worse in NYC by a geographical phenomenon known as the “Urban Heat Island effect (UHI),” which raises temperatures between 1 and 5 degrees higher than the surrounding rural areas. These higher average temperatures in growing urban areas—especially with their increasing elderly populations—project more intense, frequent, and longer heat waves making heat an urgent environmental and health challenge. Extreme heat can also stress infrastructure, like electrical transmission lines, railroad tracks, and airport runways. In addition to increasing risks to human, animal, and ecosystem health, prolonged periods of extreme heat increase energy demand for cooling using air conditioners, producing more greenhouse gas emissions and worsening future warming and climate change.

The Heat Vulnerability Index

To help identify NYC’s most heat-vulnerable neighborhoods, Columbia University and the NYC Department of Health and Mental Hygiene (DOHMH) developed a Heat Vulnerability Index (HVI) that combines metrics proven to be strong indicators of heat risk through validation with health data and that describes both social and physical characteristics.

The Heat Vulnerability Index is a tool that is used to measure and assess a community's vulnerability to extreme heat events. It takes into account a variety of factors, such as the average temperature in an area, the availability of air conditioning, and the demographic makeup of the community.

The Heat Vulnerability Index is considered to be a good tool for several reasons. First, it provides a comprehensive and objective measure of a community's vulnerability to extreme heat. This can help policymakers and other decision makers identify areas that are at higher risk and target resources and support to those areas.

Second, the heat vulnerability index can be used to compare different communities and identify trends and patterns in vulnerability to extreme heat. This can help identify which communities are most at risk and where interventions may be needed.

Third, the heat vulnerability index can be updated and refined over time as new data becomes available. This allows for a more accurate and up-to-date assessment of a community's vulnerability to extreme heat.

Credit: Department of Health and Mental Hygene, 2015

Photo of Refreshing Waters outdoor cooling station in Hunts Point. Photo Credit: Dean Kaufman

Using the Heat Vulnerability Index for Cooling Center Equity

Cooling centers offer vital, life-saving spaces for people to access air conditioning during heat waves. However, cooling centers are not located equitably across neighborhoods. A report analyzing cooling center availability during the weeklong heat wave from July 19-25th, 2022 painted a picture of disparities in cooling center access to New Yorkers across the Five Boroughs.

These were their key findings:

East Flatbush was significantly underserved by cooling centers, with only two open cooling centers available to its 162,400 residents.
The top 10 neighborhoods with the highest heat vulnerability (HVI 4 and 5) and lowest number of cooling centers per 100,000 people were: East Flatbush, Elmhurst and Corona, Kingsbridge Heights and Bedford, Kew Gardens and Woodhaven, Crown Heights and Prospect Heights, Borough Park, South Crown Heights, and Lefferts Gardens, Bedford Stuyvesant, Fordham, and University Heights, and Highbridge and Concourse.
Queens had the lowest number of cooling centers per 100,000 people (5.0), while Manhattan has the highest (7.1).
Half of all cooling centers were listed as being closed on Saturdays, and 83% were listed as being closed on Sundays—even while the weeklong July 2022 heat emergency spanned the course of a weekend.
Nearly half of the City’s activated cooling centers were senior centers, only open to people over 60 years old. Of those senior cooling centers, 56% did not offer extended hours and 22% did not have wheelchair access.

A map of cooling centers in NYC, Credit: EPA & Esri

The Heat Vulnerability Index is used to identify which neighborhoods aren't being provided with enough cooling center access for their population. The Index found that during the heat wave in July, more vulnerable communities had significantly less service than less vulnerable communities.

Some solutions that would abate this problem in NYC include:

Increase the number of cooling center locations in the most underserved neighborhoods, starting with East Flatbush.
Expand alternate cooling center siting options, especially in underserved neighborhoods. Establish outdoor cooling stations.
Increase extended and weekend hours, especially in heat-vulnerable neighborhoods.
Make cooling center information permanently available to enable proactive emergency planning.
Ensure all cooling centers are wheelchair accessible.
Transition to more sustainable cooling systems.
Reduce urban heat island effect with more green spaces and cool pavements in heat-vulnerable neighborhoods.

Now, cooling center accessibility issues and the solutions brought are only a single result of what can happen when we use the Heat Vulnerability Index. Cooling centers without wheelchair accessibility? Closed on Sunday? These are easy to identify and address, with the HVI in our hands, and we can identify which specific areas need green infrastructure and attention, rather than investing resources into less vulnerable neighborhoods.

Moving forward with the HVI

New York City is in the midst of a green renaissance. Sustainable buildings, cooling rooves, pavements, electric vehicles, countless urban green infrastructure projects, you name it. In 2018, the Mayor's Office of Resiliency had a 100-million-dollar “Cool Neighborhoods NYC” initiative that addresses more heat-vulnerable neighborhoods through targeted tree planting along streets and parks, cool roof programs, and the implementation of the Be A Buddy program, where residents have “buddies” that they check on during extreme weather events (usually senior citizens and individuals with disabilities). The NYC Mayor’s Office of Resiliency used the results of the Heat Vulnerability index in collaboration with the NYC Department of Health and Mental Hygiene and Columbia University to direct cool design interventions and tailor heat resilience social programs. This is just the start.

The "Cool Neighborhoods NYC" initiative was a leap in the right direction, and the nation is following suit. Upper-tier cities like Philadelphia, Baltimore, and Washington D.C, along with lower-tier cities like Harrisburg, Albany, and Bridgeport are addressing their own Urban Heat Island effects in similar manners to New York.

The red spots are urban landscape, areas now addressing their own UHI effect issues

As 2022 comes to a close, the Urban Heat Island effect is now a central issue for policymakers and urban designers in urban cities as temperatures rise globally. While UHI is being addressed everywhere in the United States, we have a unique tool with the Heat Vulnerability Index to attack underserved areas and improve the daily lives of the residents in our cities. If we use the HVI appropriately, we can surely see a decrease in heat-related ER visits and deaths, lower demand for cooling in warmer months, along with more equitable treatment for more vulnerable neighborhoods not only in New York City but all urban cities in America.

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