Nav: Home

New model helps explain seasonal variations in urban heat islands

March 24, 2020

DURHAM, N.C. -- Scientists have devised a simple new model that explains how the undesirable effects of urban heat islands vary across seasons. Their results could help cities in different climatic regions design heat mitigation strategies.

Unlike existing urban climate models which require a large amount of information and are computationally very demanding, the new coarse-grained model provides general insights into how seasonal changes in rainfall, solar radiation, and vegetation conditions of an urban environment affects the intensity and timing of surface urban heat islands at a city-wide scale.

"With just two equations, our model can describe all these complex interactions," said Gabriele Manoli, a lecturer in environmental engineering at University College London, who led the research.

"For city planners, it provides a new approach that complements more detailed, city-specific tools, and provides general guidelines on the effects of heat mitigation strategies, such as increasing green spaces, in different climates and during different times of the year," Manoli said. "Because of its simplicity, our framework can be applied to cities where extensive data and detailed simulations are not available."

For scientists, the model provides new evidence that seasonal variations in the intensity of urban-rural surface temperature differences -- which, until now, have been observed but not clearly explained -- are controlled by time lags between solar radiation, temperatures, and rainfall, Manoli said.

If solar radiation occurs in conjunction with water availability, summer conditions cause strong surface urban heat island intensities due to high rates of evaporative cooling in surrounding rural areas. The rural areas grow cooler by a few degrees, while the urban area, where impervious and heat-absorbing surfaces can limit the effect of evaporative cooling, grows much warmer. This is typically what we see in cities like Paris or London, which are in climates with relatively wet summers.

"This can have major implications for local energy consumption, climate adaptation policies, and public health, especially heat-related mortalities," said Gabriel Katul, Theodore S. Coile Distinguished Professor of Hydrology and Micrometeorology at Duke University.

But in cities where rainfall is scarce during summer, such as Phoenix or Madrid, the opposite effect can occur. With less rainfall and vegetation to spur cooling, rural areas heat up and the city experiences an "oasis effect" in which, though it may still be blisteringly hot, it's nonetheless one or two degrees cooler than the surrounding countryside.

"These seasonal patterns of warming and cooling have significant implications for heat mitigation strategies, as urban green spaces can reduce heat island intensity during summer, while potentially negative effects during winter of albedo management, e.g. painting streets of white, are mitigated by the seasonality of solar radiation," Katul noted.

Rising temperatures and shifting rainfall patterns linked to climate change may alter the seasonality of urban heat islands in coming decades, he said. Further research is needed in that direction.

Manoli and Katul developed the new model with Simone Fatichi of ETH Zurich and Elie Bou-Zeid of Princeton University.
-end-
They published their peer-reviewed research March 16 in the Proceedings of the National Academy of Sciences. Funding came from the Branco Weiss Fellowship--Society in Science, the U.S. Army Research Office and the U.S. National Science Foundation.

CITATION: "Seasonal Hysteresis of Surface Urban Heat Islands," Gabriele Manoli, Simone Fatichi, Elie Bou-Zeid and Gabriel Katul; March 16, 2020, Proceedings of the National Academy of Sciences. DOI: https://doi.org/10.1073/pnas.1917554117

Duke University

Related Climate Change Articles:

Mysterious climate change
New research findings underline the crucial role that sea ice throughout the Southern Ocean played for atmospheric CO2 in times of rapid climate change in the past.
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.
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

Sound And Silence
Sound surrounds us, from cacophony even to silence. But depending on how we hear, the world can be a different auditory experience for each of us. This hour, TED speakers explore the science of sound. Guests on the show include NPR All Things Considered host Mary Louise Kelly, neuroscientist Jim Hudspeth, writer Rebecca Knill, and sound designer Dallas Taylor.
Now Playing: Science for the People

#576 Science Communication in Creative Places
When you think of science communication, you might think of TED talks or museum talks or video talks, or... people giving lectures. It's a lot of people talking. But there's more to sci comm than that. This week host Bethany Brookshire talks to three people who have looked at science communication in places you might not expect it. We'll speak with Mauna Dasari, a graduate student at Notre Dame, about making mammals into a March Madness match. We'll talk with Sarah Garner, director of the Pathologists Assistant Program at Tulane University School of Medicine, who takes pathology instruction out of...
Now Playing: Radiolab

Kittens Kick The Giggly Blue Robot All Summer
With the recent passing of Ruth Bader Ginsburg, there's been a lot of debate about how much power the Supreme Court should really have. We think of the Supreme Court justices as all-powerful beings, issuing momentous rulings from on high. But they haven't always been so, you know, supreme. On this episode, we go all the way back to the case that, in a lot of ways, started it all.  Support Radiolab by becoming a member today at Radiolab.org/donate.