Featured Research

from universities, journals, and other organizations

Ecosystem, vegetation affect intensity of urban heat island effect

Date:
January 5, 2010
Source:
NASA/Goddard Space Flight Center
Summary:
Researchers studying urban landscapes have found that the intensity of the "heat island" created by a city depends on the ecosystem it replaced and on the regional climate. Urban areas developed in arid and semi-arid regions show far less heating compared with the surrounding countryside than cities built amid forested and temperate climates.

NASA researchers studying urban landscapes have found that the intensity of the "heat island" created by a city depends on the ecosystem it replaced and on the regional climate. Urban areas developed in arid and semi-arid regions show far less heating compared with the surrounding countryside than cities built amid forested and temperate climates.

Related Articles


"The placement and structure of cities -- and what was there before -- really does matter," said Marc Imhoff, biologist and remote sensing specialist at NASA's Goddard Space Flight Center in Greenbelt, Md. "The amount of the heat differential between the city and the surrounding environment depends on how much of the ground is covered by trees and vegetation. Understanding urban heating will be important for building new cities and retrofitting existing ones."

Goddard researchers including Imhoff, Lahouari Bounoua, Ping Zhang, and Robert Wolfe presented their findings on Dec. 16 in San Francisco at the Fall Meeting of the American Geophysical Union.

Scientists first discovered the heat island effect in the 1800s when they observed cities growing warmer than surrounding rural areas, particularly in summer. Urban surfaces of asphalt, concrete, and other materials -- also referred to as "impervious surfaces" -- absorb more solar radiation by day. At night, much of that heat is given up to the urban air, creating a warm bubble over a city that can be as much as 1 to 3°C (2 to 5°F) higher than temperatures in surrounding rural areas.

The impervious surfaces of cities also lead to faster runoff from land, reducing the natural cooling effects of water on the landscape. More importantly, the lack of trees and other vegetation means less evapotranspiration -- the process by which trees "exhale" water. Trees also provide shade, a secondary cooling effect in urban landscapes.

Using instruments from NASA's Terra and Aqua satellites, as well as the joint U.S. Geological Survey-NASA satellite Landsat, researchers created land-use maps distinguishing urban surfaces from vegetation. The team then used computer models to assess the impact of urbanized land on energy, water, and carbon balances at Earth's surface.

When examining cities in arid and semi-arid regions -- such as North Africa and the American Southwest -- scientists found that they are only slightly warmer than surrounding areas in summer and sometimes cooler than surrounding areas in winter.

In the U.S., the summertime urban heat island (UHI) for desert cities like Las Vegas was 0.46°C lower than surrounding areas, compared to 10°C higher for cities like Baltimore. Globally, the differences were not as large, with a summertime UHI of -0.21°C for desert cities compared to +3.8°C for cities in forested regions.

In a quirk of surface heating, the suburban areas around desert cities are actually cooler than both the city center and the outer rural areas because the irrigation of lawns and small farms leads to more moisture in the air from plants that would not naturally grow in the region.

"If you build a city in an area that is naturally forested -- such as Atlanta or Baltimore -- you are making a much deeper alteration of the ecosystem," said Imhoff. "In semi-arid areas with less vegetation -- like Las Vegas or Phoenix -- you are making less of a change in the energy balance of the landscape."

"The open question is: do changes in land cover and urbanization affect global temperatures and climate?" Imhoff added. "Urbanization is perceived as a relatively small effect, and most climate models focus on how the oceans and atmosphere store and balance heat. Urban heat islands are a lot of small, local changes, but do they add up? Studies of the land input are still in early stages."


Story Source:

The above story is based on materials provided by NASA/Goddard Space Flight Center. Note: Materials may be edited for content and length.


Cite This Page:

NASA/Goddard Space Flight Center. "Ecosystem, vegetation affect intensity of urban heat island effect." ScienceDaily. ScienceDaily, 5 January 2010. <www.sciencedaily.com/releases/2009/12/091215173021.htm>.
NASA/Goddard Space Flight Center. (2010, January 5). Ecosystem, vegetation affect intensity of urban heat island effect. ScienceDaily. Retrieved November 27, 2014 from www.sciencedaily.com/releases/2009/12/091215173021.htm
NASA/Goddard Space Flight Center. "Ecosystem, vegetation affect intensity of urban heat island effect." ScienceDaily. www.sciencedaily.com/releases/2009/12/091215173021.htm (accessed November 27, 2014).

Share This


More From ScienceDaily



More Earth & Climate News

Thursday, November 27, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Scientists Find Invisible Space Shield Protecting Earth

Scientists Find Invisible Space Shield Protecting Earth

Newsy (Nov. 27, 2014) — An invisible barrier is keeping dangerous super fast electrons from interfering with our atmosphere, but scientists aren't entirely sure how. Video provided by Newsy
Powered by NewsLook.com
Bolivian Recycling Initiative Turns Plastic Waste Into School Furniture

Bolivian Recycling Initiative Turns Plastic Waste Into School Furniture

Reuters - Innovations Video Online (Nov. 26, 2014) — Innovative recycling project in La Paz separates city waste and converts plastic garbage into school furniture made from 'plastiwood'. Tara Cleary reports. Video provided by Reuters
Powered by NewsLook.com
Blu-Ray Discs Getting Second Run As Solar Panels

Blu-Ray Discs Getting Second Run As Solar Panels

Newsy (Nov. 26, 2014) — Researchers at Northwestern University are repurposing Blu-ray movies for better solar panel technology thanks to the discs' internal structures. Video provided by Newsy
Powered by NewsLook.com
Antarctic Sea Ice Mystery Thickens... Literally

Antarctic Sea Ice Mystery Thickens... Literally

Newsy (Nov. 25, 2014) — Antarctic sea ice isn't only expanding, it's thicker than previously thought, and scientists aren't sure exactly why. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:

Strange & Offbeat Stories

 

Plants & Animals

Earth & Climate

Fossils & Ruins

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins