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The Urban Heat Index Unveiled

July 28, 2022

Summer in Houston, Texas, is hot. Average temperatures measure slightly warmer than in Death Valley, making it one of the hottest places in America. While no one’s making it through a Houston summer without sweating, some residents suffer more than others because heat stalls in their neighborhood forming an even hotter pocket known as an urban heat island. [photo courtesy of Tom Wang]

Take, for example, the highly diverse and densely populated neighborhood of Alief in Southwest Houston. Alief’s nighttime temperatures in July average 82 degrees Fahrenheit, compared to the city’s overall average of 79.4 degrees. The higher temperatures can raise energy bills, levels of air pollution, and heat-related illnesses in a neighborhood already struggling with high asthma rates and energy burdens. That’s why Greenlink Analytics recently developed a new and novel data set examining Urban Heat Intensity for the country’s largest metro areas.

“Our Urban Heat Index translates a census tract’s temperatures into a severity score from 1 to 10 relative to other tracts in the city," says Sharanya Madhavan, lead data scientist for Greenlink’s UHI project. “By looking at different temperatures, we can better understand the urban heat island effect, identify the neighborhoods disproportionately affected by heat, and begin to see the relationship between heat and other burdens.”


The average Urban Heat Intensity score in Houston is 5.9. Alief’s is 10, meaning it has a high heat island effect and is disproportionately hotter than other neighborhoods around them. Here’s how we arrived at that number. Greenlink Analytics utilized satellite imagery to capture nighttime temperature for the 379 largest

[Image: Urban Heat Index for Houston] metropolitan areas in the United States


down to the resolution of one square kilometer. Temperatures were analyzed for the hottest months of the year – May through August..

It’s the next step of scrutiny that sets the data apart. Greenlink analyzed temperature gaps from month to month to pinpoint the month with the largest heat disparities in each city. In Houston, it’s July. In Atlanta it’s May. In Denver it’s August. The goal was to assess the disparities in heat burdens, says Madhavan, since the data shows people having very different experiences related to heat within the same city and month. The month with the highest temperature differential was then converted to a heat intensity score using a percentile system. This allows each city to better understand how any neighborhood compares to others.

“This data can help inform policies that reduce heat islands and alleviate the cascade of burdens that accompany extreme heat, such high energy burden and asthma rates, making life harder to handle and bear,” says Madhavan.


Many city neighborhoods across the country have a high heat island effect. Urban heat islands form when cities cover land with buildings, concrete, asphalt, and other solid surfaces in population dense places. These hardscapes absorb the sun’s heat during the day and refract it at night, keeping the area hotter than normal. Low-income neighborhoods are frequently hotter than wealthier ones due to systemic differences in the way the communities are designed, developed, and maintained.


Relevant data is vital for addressing the disproportionate burden heat can cause. The Urban Heat Intensity data set will launch inside the Greenlink Equity Map the first week of August 2022.