Nav: Home

Heat waves hit heat islands hardest

September 28, 2015

MADISON -- Extreme summers like that of 2012 -- which saw record temperatures in cities across the U.S. -- may be atypical, but experts say they will return, especially as the planet warms under climate change. And as they do, cities will be especially vulnerable.

A new University of Wisconsin-Madison study details how extreme temperatures affect urban heat islands -- densely built areas where heat-retaining asphalt, brick and concrete make things hotter than their nonurban surroundings.

The study, published last week in the journal Environmental Research Letters, found heat waves hit urban areas hardest, shedding light on what a future with more extreme summers might mean for the world's growing population of urbanites.

Since heat islands tend to be the most densely populated areas of the city, as the chances of a heat wave rise, many city-dwellers could face more uncomfortable summers, increased health risks and potentially higher energy bills from air conditioning.

"Not only do heat waves intensify the urban heat island, but the heat island also intensifies the heat wave, which is pretty much the opposite of what you'd want," says the study's lead author, Jason Schatz, a postdoctoral researcher on the Water Sustainability and Climate Project at UW-Madison.

By nature, extremes are rare. But Schatz got a stroke of luck when, within the first three years of the study, their study site and Wisconsin's capital city, Madison, was hit with both the 2012 heat wave and the polar vortex of 2013-14, which caused the coldest winter in 35 years.

Using data from the 150 sensors Schatz installed in and around Madison, the researchers found that urban areas experienced up to twice as many hours over 90 degrees Fahrenheit than rural areas during the 2012 heat wave.

The densest urban areas also spent over four consecutive nights in temperatures above 80, the National Weather Service's nighttime heat advisory threshold. Since prolonged heat exposure, rather than isolated hot days, is what can cause heat stress, long stretches with no nighttime reprieve in densely populated areas pose a greater risk to public health.

This risk is bound to grow if cities don't plan accordingly, warns co-author Chris Kucharik, a professor in the Department of Agronomy and the Nelson Institute for Environmental Studies.

"2012 is pretty representative of summers we are likely to experience 50 years from now," he says.

Climate change projections from the Wisconsin Initiative on Climate Change Impacts indicate Madison could experience an average of 29 to 37 days above 90 degrees by the middle of this century, compared to the current average of 9 days. Yet these projections don't account for urban heat island effects, upon which Schatz casts concern.

"Cities are where most people will encounter future warming, and projections are underestimating the amount of heat urban communities need to prepare for," he says.

It's not just climate change projections that underestimate the effects of the urban heat island, Schatz says. Madison's only National Weather Service station, located at the Dane County Regional Airport, is also undershooting.

The airport recorded 39 days over 90 degrees in 2012, but the data Schatz collected indicated downtown Madison experienced upwards of 49 days over 90.

"The airport is in a low-lying, swampy area, which isn't representative of where most of Madison's population lives," says Schatz.

On the flip side, the heat island could make urban life a little easier when temperatures dive to the other end of the thermometer. During the polar vortex, Madison's heat islanders experienced as many as 40 percent fewer hours of exposure to below-zero temperatures, making it slightly less miserable on both their bodies and heating bills.

Cold snaps of this magnitude are less likely to happen as Wisconsin warms, but Schatz says understanding what they do to the urban climate is still important.

"This is Wisconsin. Cold weather still happens," he says.
The study builds on a 2014 paper from Schatz and Kucharik in the Journal of Applied Meteorology and Climatology describing the seasonal behavior of Madison's urban heat island. Their research is supported by the Water Sustainability and Climate project, a research endeavor funded by the National Science Foundation.

CONTACT: Jason Schatz, 608-207-944-0021,; Chris Kucharik, 608-890-3021 or 608-263-1859,

Jenny Seifert,, 608-512-6259

University of Wisconsin-Madison

Related Climate Change Articles:

Mapping the path of climate change
Predicting a major transition, such as climate change, is extremely difficult, but the probabilistic framework developed by the authors is the first step in identifying the path between a shift in two environmental states.
Small change for climate change: Time to increase research funding to save the world
A new study shows that there is a huge disproportion in the level of funding for social science research into the greatest challenge in combating global warming -- how to get individuals and societies to overcome ingrained human habits to make the changes necessary to mitigate climate change.
Sub-national 'climate clubs' could offer key to combating climate change
'Climate clubs' offering membership for sub-national states, in addition to just countries, could speed up progress towards a globally harmonized climate change policy, which in turn offers a way to achieve stronger climate policies in all countries.
Review of Chinese atmospheric science research over the past 70 years: Climate and climate change
Over the past 70 years since the foundation of the People's Republic of China, Chinese scientists have made great contributions to various fields in the research of atmospheric sciences, which attracted worldwide attention.
A CERN for climate change
In a Perspective article appearing in this week's Proceedings of the National Academy of Sciences, Tim Palmer (Oxford University), and Bjorn Stevens (Max Planck Society), critically reflect on the present state of Earth system modelling.
Fairy-wrens change breeding habits to cope with climate change
Warmer temperatures linked to climate change are having a big impact on the breeding habits of one of Australia's most recognisable bird species, according to researchers at The Australian National University (ANU).
Believing in climate change doesn't mean you are preparing for climate change, study finds
Notre Dame researchers found that although coastal homeowners may perceive a worsening of climate change-related hazards, these attitudes are largely unrelated to a homeowner's expectations of actual home damage.
Older forests resist change -- climate change, that is
Older forests in eastern North America are less vulnerable to climate change than younger forests, particularly for carbon storage, timber production, and biodiversity, new research finds.
Could climate change cause infertility?
A number of plant and animal species could find it increasingly difficult to reproduce if climate change worsens and global temperatures become more extreme -- a stark warning highlighted by new scientific research.
Predicting climate change
Thomas Crowther, ETH Zurich identifies long-disappeared forests available for restoration across the world.
More Climate Change News and Climate Change Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Listen Again: Reinvention
Change is hard, but it's also an opportunity to discover and reimagine what you thought you knew. From our economy, to music, to even ourselves–this hour TED speakers explore the power of reinvention. Guests include OK Go lead singer Damian Kulash Jr., former college gymnastics coach Valorie Kondos Field, Stockton Mayor Michael Tubbs, and entrepreneur Nick Hanauer.
Now Playing: Science for the People

#562 Superbug to Bedside
By now we're all good and scared about antibiotic resistance, one of the many things coming to get us all. But there's good news, sort of. News antibiotics are coming out! How do they get tested? What does that kind of a trial look like and how does it happen? Host Bethany Brookeshire talks with Matt McCarthy, author of "Superbugs: The Race to Stop an Epidemic", about the ins and outs of testing a new antibiotic in the hospital.
Now Playing: Radiolab

Dispatch 6: Strange Times
Covid has disrupted the most basic routines of our days and nights. But in the middle of a conversation about how to fight the virus, we find a place impervious to the stalled plans and frenetic demands of the outside world. It's a very different kind of front line, where urgent work means moving slow, and time is marked out in tiny pre-planned steps. Then, on a walk through the woods, we consider how the tempo of our lives affects our minds and discover how the beats of biology shape our bodies. This episode was produced with help from Molly Webster and Tracie Hunte. Support Radiolab today at