CGU4U/C
Unit 3: Sustainability in the Global Environment
Heat, Pollution, and Skyscrapers Make Cities Have
More Thunderstorms
Atlanta. Eyebeam Photography/Getty Images
Ah, city life: The culture! The food! The music! The thunderstorms!
Wait, what? Thunderstorms? Yes, that’s right: You can add
weather to the list of things that are more exciting in the city than
in the sticks.
Ok, not all cities. But in regions like the American south, normal
urban attributes like heat, pollution, and tall buildings could stir up
more storms. New research examined nearly two decades of
meteorological data from Georgia and found thunderstorms were
slightly more likely to form over Atlanta than the surrounding rural
areas. Through modeling and other research, meteorologists have known about the connection between cities
and storms for decades, but this is the first time data has shown the phenomena in action.
During the summer, cumulonimbus clouds ripen like peaches over Georgia and Alabama. These moisture-heavy
storms appear on radars as dark, pixellated patterns. Alex Haberlie, a geography doctoral student at Northern
Illinois University, used a computer program to find these patterns, then crunched 17 years worth of data. In
all, the geographers that found Atlanta is 5 percent more likely to initiate a thunderstorm than the surrounding
rural area.
“By our count, that’s a couple to three or more storms a year,” Haberlie, the study’s lead author, says. This
doesn’t seem like much, but a city’s built infrastructure compounds the effects of any storm. For instance,
Atlanta’s catastrophic 2009 floods probably were worsened because all the asphalt and concrete kept the
water from seeping into the soil.
“The discovery that urban environments can create their own storms and rainfall: Not new at all,” says J.
Marshall Shepherd, a researcher at the University of Georgia who is an expert in urban meteorology.
Researchers have long known that cities generally get more rainfall than their surrounding areas. Shepherd
says that he and other researchers teased out the relationship between cities and thunderstorms by running
models. “Set up studies where you don’t include Atlanta, and some where you do, and lo and behold you can
see that taking away the city reduces the rainfall,” he says. Based on research he’s seen, Shepherd says he isn’t
surprised by the 5 percent difference between Atlanta and its realm. He expected the number to be upward of
20 percent. But despite his misgivings about the degree of difference shown in the current study’s results, he
says what’s really important is that their methods show that these effects are actually happening.
According to Shepherd and Haberlie, these storms are brewed by several factors. First, cities are hotter than
surrounding areas. This warm, rising city air creates circulation that mixes with other atmospheric conditions to
create thunderheads. Second, tall buildings form a barrier that pushes wind up and around the city. “Upward
motion is always good for thunderstorms,” says Haberlie. Finally, pollution particles act like condensation
nuclei that water glom onto, creating droplets. In essence, cities get more thunder and rain because they are
hot, stale, and dirty.
But you can’t generalize this type of research to every city. Places like New York, Chicago, and Washington D.C.
are probably also contributing to their own thunderstorms, but because these cities are so close to large bodies
of water, it would be hard to tease this out of radar data the way Haberlie and his co-authors did with Atlanta.
Research like this could help city managers plan for bigger influxes of water, either by opening up more
reservoirs, or coming up with better strategies for flooding. But perhaps most important, there is no telling if
this research will result in a long-awaited new verse to the AC/DC classic, “Thunderstruck.”
CGU4U/C
Unit 3: Sustainability in the Global Environment
Questions:
1. What are 3 ways the built environment increases the likelihood of a thunderstorm occurring?
Increased temperatures cause less dense hot air to rise and condense as rainfall
Pollution and dust particles act as condensation nuclei that collect water vapor and fall as raindrops
Tall buildings force air higher into the atmosphere to cool and condense as rain
2. Considering that flooding is a problem in Atlanta, and the built environment is contributing to
increased rainfall, what can urban planners do to make the city more sustainable and less likely to
flood? ( hint: what did L.A do?)
Design the urban landscape to absorb water rather than collect and channel it in sewers. More rain means
more sewer infrastructure unless the water is absorbed.
THE URBAN HEAT ISLAND
How does the urban heat island form?
urban regions to become warmer than their rural
surroundings, forming an "island" of higher
temperatures in the landscape.
How do they change throughout the day?
Both day and night are warmer than the surrounding landscape. But nights are even
warmer in comparison than days are due to the heating of that day.
Why do we care about heat islands?
Increased energy consumption:
Elevated emissions of air pollutants and greenhouse gases:
Compromised human health and comfort:
Impaired water quality:
What can be done to limit the effect?

increasing

creating

installing
tree and vegetative cover;
green roofs (also called "rooftop gardens" or "eco-roofs");
cool—mainly reflective—roofs; and
CGU4U/C

using
Unit 3: Sustainability in the Global Environment
cool pavements.
How do aspects of the Built Environment Impact the urban heat Island?
1.Which urban structures/ zones contribute
highest to the heat island?
Downtown core and concrete covered
areas
Why?
These areas absorb solar radiation and
Re-radiate it as heat
2. Which structures/zones contribute the
least to the heat island?
Ponds, treed areas and parks. Less concrete structures
Why?
Trees absorb and use energy to evaporate water. Ponds and water have a high heat capacity which means it
absorbs the sunlight but does not turn it into heat.
3. How do climate scientists and geographers collect their temperature data when studying the urban heat
island? What technology is employed?
Remote sensing satellites continuously collect information about absorbed and reflected sunlight.
Infrared sensors detect heat & temperature changes
Connection back to unit 1:
Is this continuous or non-continuous data? When mapped is it best represented by vector or raster data?
Continuous and is best represented by raster ( pixel) data
What factors/ conditions/ errors complicate a researcher’s ability to collect accurate heat island data?
Temperature is measuring from multiple sites and recording technologies ( sometimes they don’t agree)
CGU4U/C
Unit 3: Sustainability in the Global Environment
Specifics of the built environment and natural environment make it complicated to get consistent results.
Does urban heat island play a significant role in local, regional or global climate change? Where if so.
LOCAL yes , regional minor, global NO
The urban heat island does not cause global warming !!!