UHI@UT

the Urban Heat Island Group at UT Austin

Civil, Architectural, and Environmental Engineering Department

 
Take the Tour

Hi! Nice to meet you.

We're all undergrads at UT Austin. (Click our pics to find out more!)

 

Professor Lance Manuel and a shared interest in Austin's urban heat island brought us together - and now we want to share that interest with you!

 
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Overview

So what is an urban heat island ? In a general sense, it's a phenomenon in which developed areas experience higher temperatures than less developed areas nearby.

For example, Austin probably experiences higher average temperatures than Lago Vista, a nearby town that's much smaller and less urbanized.

So what causes an urban heat island? As urban features like buildings, highways, and paving reduce or replace natural features, like bodies of water and vegetation, an area's temperatures rise compared to undeveloped areas.

Let's explore the causes of heat islands in more detail...

Causes

Causes

Heat islands are caused by many variables. A few significant ones are

  • impervious cover (e.g., pavement, asphalt)
  • development
  • arrangement of buildings
  • sky view factor
  • population
  • weather

For example, with an increase in impervious cover , there's an associated decrease in vegetation. But impervious cover doesn't absorb water like vegetation does, leading to an increase in run-off water. Plus, while vegetation can cool air by evapotranspiration, impervious cover heats air!

Certain building materials that have a low albedo (or solar reflectivity) also contribute to heat island effects. Rather than reflecting solar radiation, a lot of building materials absorb it and then emit heat to their surroundings.

But wait - how do we know heat islands exist? Let's take a look at the data!

Data

Data

Heat islands can be studied using satellite imagery, which allows researchers to visualize and analyze the energy reflected and emitted from Earth's surface. Instruments on satellites can measure the thermal energy emitted from surfaces as wavelengths, creating thermal images, on which colors are associated with temperatures. By comparing thermal images of developed and undeveloped areas, the urban heat island effect can be quantified - simply take the difference between the temperatures of different areas and map the results.

One source of satellite images is NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS). On board the Terra and Aqua satellites, MODIS is able to capture images of and data from the Earth’s entire surface every 1 to 2 days. In addition, MODIS can help with obtaining historical data, helping us to understand how urban heat islands have evolved.

After collecting relevant satellite images, information can be plotted on a coordinate system, like ArcGIS, to create a visual representation of where the peak temperature differential occurs. A heat map of the city can be created and a fundamental heat island can be visualized.

Now that we know a little about heat islands, why should we care about them?

Impacts
 

Heat Island Impacts

 

Energy

Increased energy and peak energy demands, leading to brownouts.

Pollution

More energy demand = more toxic pollution and carbon emissions.

Health+Comfort

Hotter cities can be uncomfortable and dangerous.

Water

Hot runoff water harms aquatic life.

 

So heat islands have a lot of negative impacts on people and our environment.

Let's investigate how heat islands impact our health.

Health
 

Health

Urban heat islands cause both an increase in temperature as well as in air and water pollution. This results in major health issues in addition to general discomfort for urban residents.

Heat islands can contribute to respiratory issues, heat stroke, water-borne illnesses, and even mortality. The elderly and the ill are especially vulnerable sectors of the population. Low-income urban residents are also in a vulnerable position if they lack access to air conditioning, healthy buildings, and healthcare.

If you'd like to read more in-depth about heat islands' impact on mortality, we encourage you to look at this recent study on climate-mortality relationships in the US, or at this study specific to Washington, D.C.

In many ways, heat islands are a human issue.

So our next question has to be - what can we do about heat islands?

Mitigation
 
 
 

Heat Island Mitigation

 

Plants

Increased vegetation - looks good, reduces runoff, and can lower temperatures.

Build Smart

Use reflective building and paving materials.

Shading

Add shading to buildings and outdoor areas.

Energy

Reduce your energy use.

 

So there are strategies we can implement to mitigate the effects of heat islands. Of course, some strategies may be more effective for certain places - what's best for our city, Austin?

Our Project
 

Our Project

 

Our goal is to quantify and model the urban heat island effect in Austin.

Currently, we're conducting a comprehensive literature review and evaluating accessible sources of data.

As we progress, check back for updates.

 

If you'd like to get in touch with us, find our contact information here.

Contact
 

If you'd like to know even more about UHIs, please look at the resources below.

Resources

 
 

Resources

 
 

EPA

A great series of guides to heat island effects.

LBLI

Lawrence Berkeley National Laboratory's Heat Island Group.

City of ATX

Local government efforts.

 
 
 
 

Get in touch!

 
 
 
 

We'd love to hear from you.

 
 
 

This website built by Gitanjali Bhattacharjee, with help from Bootply. Text also contributed by Lauryn Altena, Tarek El-Afifi, Lilian Gonzalez.

Images are credited by being linked to their sources.

Website (excluding images) © Gitanjali Bhattacharjee 2015.