Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Spring through fall, cities are greener longer than neighboring rural regions

29.07.2004


BU team shows so-called urban heat island effect influences onset of ’greenup,’ dormancy



Summer can sometimes be a miserably hot time for city dwellers, but new research shows that an urban setting allows plants to bask in a hot-house environment that keeps them greener longer.

Recent NASA-sponsored research from a team of geographers in Boston University’s Center for Remote Sensing shows that the growing season for vegetation in about 70 urban areas in North America is, on average, 15 days longer than that in rural regions surrounding the cities studied. Led by Xiaoyang Zhang, a research assistant professor in BU’s Geography Department, the team found that, like many urban-dwelling humans, urban greenery lives at a more intense pace, getting as much as a seven-day jump-start on spring and up to eight additional days before winter dormancy than vegetation in surrounding rural areas.


This happens largely because the asphalt, steel, exhaust, and other environmental changes introduced by humans contribute to what is known as the urban heat island effect. The researchers found this influence to be far-reaching. Taken together, the heat island effect for the areas studied ripples beyond urban boundaries to create an ecological "footprint" 2.4 times greater than that of urban land use in eastern North America.

Their analyses also show that changes in land surface temperatures and when vegetation first becomes green are not significantly related to urban size, leading the team to speculate that factors related to population density may play the more important role in the observed effects. The data do, however, show that "greenup" changes in surrounding rural areas are linked to city size -- the larger the city, the longer the reach of the extended greenup effect.

To date, more than one-third of the land surface of Earth has been transformed by human activities. These changes have not only altered the look of the land, but, according to a growing body of research, have also affected climate and significantly changed Earth’s ecosystems. In an attempt to determine the effect that the urban heat island phenomenon has on the growing season for urban vegetation, the BU team used satellite data to evaluate when vegetation in urban and rural settings first became green and then when it entered dormancy, thereby ending one season’s growing cycle.

The researchers calculated the onsets of vegetation greenup and dormancy for about 70 urban areas using so-called NBAR data gathered between January 1 and December 31, 2001, by NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS). The MODIS instrument, aboard NASA satellites Terra and Aqua, gathers data on Earth’s entire surface every one to two days. The team used "nighttime lights" data and MODIS data to determine the size of the urban areas studied.

To determine the radiating effect of urban heat islands on vegetation in surrounding regions, the researchers assessed greenup data in six, two-to-three kilometer zones demarcated from urban edges. Within these zones, to a total distance of 20 km., the scientists measured land-surface temperatures and vegetation greenup responses.

They found that greenup occurs earliest in urban areas but that urban climate shows a substantial influence on vegetation growing up to 10 km. beyond the edge of urban land cover. This greenup difference is especially pronounced in the Washington, DC–Philadelphia–New York City corridor, where urban greenup occurs about 5.5 days and 8.7 days earlier than in zones 0 – 3 km. and 8 – 10 km., respectively, from the urban edge. In all, they found the strength of the urban influence decreases with distance from the perimeter of urban land cover.

Patterns in greenup onset show that urban–rural differences in vegetation response are a function of land surface temperatures, showing a significant linear trend between change in greenup and change in temperature. The trend generally shows that greenup advances three days for each one degree Celsius increase in temperature. This trend was not found for onset of dormancy, suggesting, according to the researchers, a more complex relationship that is influenced not only by temperature but also by daily exposure to light and water availability. The team’s findings are reported in a recent issue of Geophysical Research Letters.

Ann Marie Menting | EurekAlert!
Further information:
http://www.bu.edu
http://www.gsfc.nasa.gov

More articles from Earth Sciences:

nachricht Atmospheric scientists reveal the effect of sea-ice loss on Arctic warming
11.03.2019 | Institute of Atmospheric Physics, Chinese Academy of Sciences

nachricht Sensing shakes
11.03.2019 | University of Tokyo

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Self-healing coating made of corn starch makes small scratches disappear through heat

Due to the special arrangement of its molecules, a new coating made of corn starch is able to repair small scratches by itself through heat: The cross-linking via ring-shaped molecules makes the material mobile, so that it compensates for the scratches and these disappear again.

Superficial micro-scratches on the car body or on other high-gloss surfaces are harmless, but annoying. Especially in the luxury segment such surfaces are...

Im Focus: Stellar cartography

The Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) at the Large Binocular Telescope (LBT) in Arizona released its first image of the surface magnetic field of another star. In a paper in the European journal Astronomy & Astrophysics, the PEPSI team presents a Zeeman- Doppler-Image of the surface of the magnetically active star II Pegasi.

A special technique allows astronomers to resolve the surfaces of faraway stars. Those are otherwise only seen as point sources, even in the largest telescopes...

Im Focus: Heading towards a tsunami of light

Researchers at Chalmers University of Technology and the University of Gothenburg, Sweden, have proposed a way to create a completely new source of radiation. Ultra-intense light pulses consist of the motion of a single wave and can be described as a tsunami of light. The strong wave can be used to study interactions between matter and light in a unique way. Their research is now published in the scientific journal Physical Review Letters.

"This source of radiation lets us look at reality through a new angle - it is like twisting a mirror and discovering something completely different," says...

Im Focus: Revealing the secret of the vacuum for the first time

New research group at the University of Jena combines theory and experiment to demonstrate for the first time certain physical processes in a quantum vacuum

For most people, a vacuum is an empty space. Quantum physics, on the other hand, assumes that even in this lowest-energy state, particles and antiparticles...

Im Focus: Sussex scientists one step closer to a clock that could replace GPS and Galileo

Physicists in the EPic Lab at University of Sussex make crucial development in global race to develop a portable atomic clock

Scientists in the Emergent Photonics Lab (EPic Lab) at the University of Sussex have made a breakthrough to a crucial element of an atomic clock - devices...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

International Modelica Conference with 330 visitors from 21 countries at OTH Regensburg

11.03.2019 | Event News

Selection Completed: 580 Young Scientists from 88 Countries at the Lindau Nobel Laureate Meeting

01.03.2019 | Event News

LightMAT 2019 – 3rd International Conference on Light Materials – Science and Technology

28.02.2019 | Event News

 
Latest News

Molecular motors run in unison in a metal-organic framework

20.03.2019 | Life Sciences

Active substance from plant slows down aggressive eye cancer

20.03.2019 | Life Sciences

Novel sensor system improves reliability of high-temperature humidity measurements

20.03.2019 | Trade Fair News

VideoLinks
Science & Research
Overview of more VideoLinks >>>