We Need to Chill Out: Reducing the Heat Island Effect Through Design

If You Build It Poorly, Heat Will Come

 Buildings directly impact the temperature of their surroundings. To better understand this, Corgan-Hugo analyzed temperature data gathered by the National Centers for Environmental Information ¹⁶ over the last 30 years (1991-2020), from two weather stations in Dallas, Texas.  As shown in Figure 5, the weather stations A [ Dallas Love Field] and B [Redbird] are in the north and south side of the city, respectively. Weather station A is in a dense neighborhood, while weather station B is in a suburban part of the city.

Figure below shows the temperature difference recorded for these stations throughout 2023. Weather station A shows a higher recorded temperature throughout the year, reaching around 1.5 degree difference in the summertime.

This analysis aims to understand the thermal characteristics of the Dallas- Ft. Worth metroplex and the relationship between land surface temperature, vegetation, building typologies, and its effect on everyday lifestyles. This is done using a mixed mode methodology; quantitative data gathering, and qualitative insights obtained through conversations with residents in the identified zones. This dual methodology provides a comprehensive and straightforward understanding of how lifestyle choices impact various aspects of the study. The results of this analysis are intended to identify the negative impacts urban heat islands have on citizens, and ultimately help designers establish opportunities where design can play a role in reducing heat. The neighborhoods were chosen based on the 2022 NASA Eco stress heatmap of the area ¹⁷. This stratification was established according to variations in-land surface temperature.

The study area was divided into two primary zones, each representing a different level of land surface temperature. Within these zones, different neighborhood and residential zip code areas were selected based on the neighborhood and urban design of the region to have a more comprehensive selection of the whole city. The geographical distribution of these locations is visually represented in Figure 7. We chose to study four distinct locations based off the areas heat index, density level, and its proximity to downtown Dallas.

 A list of the areas selected are shown in table below.

Table 1:List of Study Areas

Using Google Earth Engine, we collected calibrated spatial land surface temperature (LST) data from satellite images. We analyzed multispectral imagery from the USGS's Landsat 8 program to calculate LST and the Normalized Difference Vegetation Index (NDVI), which measures vegetation vigor. This data will be combined with GIS parcel data to assess how different building types affect urban heat islands. After examining changes in thermal and vegetation characteristics from 2015 to 2023 , we identified specific locations with significant changes in LST and vegetation density. By understanding which urban design strategies affect heat islands positively or negatively, we believe designers can use this information to improve decision-making in urban design strategies.

We also interviewed 15 residents from each study area, which provided rich, qualitative insights to better inform the quantitative data. These responses were used to identify relationships between various demographic factors and the built environment and determine if a statistically significant association between two or more categorical variables exists.

Who Takes the Heat?

As Figure 8 shows, each neighborhood consists of a mixture of building types, such as single-family homes, duplexes, townhomes, and apartments, with sections A and D primarily consisting of single-family homes. Analyzing a variety of housing types, sheds light on the ways in which heat conditions impact residents' lives and inform strategies for creating more resilient and adaptive communities.

With a variety of building types, the study aimed to identify what, if any, correlation exists between the building type and the average LST. Figure 9 shows the average recorded LST based on the building type for all the zones. It is clear that open space and vegetated areas such as parks aide in reducing the LST of the site.

Next, using a Likert scale that ranged from 1 to 5, where 1 represented complete disagreement and 5 indicated strong agreement, the participants ranked the effect and magnitude of the summer heat wave on their behavior and everyday social life.

Table 2:  Score of Each Behavioral Question based on Are of Study

This study reveals that heat waves have significantly altered people's daily routines. Notably, the highest-rated aspect across all sections is "reduction in outdoor activities," consistently scoring above 4.5 out of 5. The figure below displays the percentage of responses based on each section's scores.

Over 90% of participants in sections A, C, and D, and over 85% in Section B, either agree or strongly agree that high temperatures have curtailed their outdoor activities.

This suggests increased indoor time, leading to higher energy consumption and potential health issues, both mentally and physically. According to the Environmental Protection Agency (EPA), indoor air pollutants are often two-to-five times higher than outdoor levels ¹⁸.

When people experience these reactions – especially those with young children – they tend to increase cooling and, consequently, electricity consumption.

During cooler times of the day, residents living in sections B and C participate in more outdoor activities. These areas have extensive outdoor green spaces such as Crawford memorial park, Trinity River Center, and Katy Trail, which tend to lower temperatures in the neighborhood, while providing areas of interest for the residents to spend their time.

Next, participants were asked to score their level of concern with heat-related issues within their communities from 1 to 5, where 1 represented least concern and 5 represented having the most concern. It is worth mentioning that the score in each of the neighborhoods separately was higher than 3.6 out of 5, with a mean of 3.87 across the board. This shows that heat-related issues are of major concern for people living in urban environments. Also, the configuration of each neighborhood plays a statistically significant role on the magnitude of behaviors in reaction to heat waves. As shown in Figure 13, the highest scores belong to sections A and D, which have the highest ratio of single-family homes in their neighborhoods compared to other zones.

These groups also represent a higher level of health concerns due to the heat surge effect between all study areas, shown in Figure 14. This underscores how urban patterns and vegetative features in the city can change the heat effect for the people living in the area.

Section D residents expressed the most concern about health and outdoor discomfort during heat surges. Figure 15 illustrates LST and NDVI indexes for each zone. In the figure, height represents LST, while color indicates NDVI values, with green indicating the highest value. Zone D notably exhibits the highest LST and lowest NDVI, which corresponds with reports from residents of reduced outdoor activity during heat waves. This highlights inadequate urban planning and building design in the area, necessitating new strategies for improvement.

Crafting effective strategies in different design scales to combat heat island and rising temperatures requires a paradigm shift in design thinking, a return to the essence of design during the renaissance and prioritizing passive solutions. In an era preceding the ubiquitous use of air conditioning, we instinctively gravitated towards passive design approaches out of necessity. Today, as we confront the challenges of escalating temperatures, there is a pressing need to rediscover and wholeheartedly adopt these time-tested strategies. Embracing passive solutions is not just a nod to tradition; it is a forward-looking initiative essential for the creation of resilient and sustainable designs to navigate the heat challenges in the years ahead.