http://www.eurekalert.org/pub_releases/2005-07/nsfc-at072005.php
Contact: Rob Gutro
[EMAIL PROTECTED]
301-286-4044
NASA/Goddard Space Flight Center--EOS Project Science Office
'Satellites and the city'
NASA satellites improve understanding of urban effects on climate and
weather
Just how does society's desire to live in densely populated areas
have the potential to change our Earth's climate? According to a new
paper, satellites can help us answer that question.
"More and more people live in cities. This means that cities will
grow rapidly over the next several decades. Evidence continues to
mount that cities affect the climate," said J. Marshall Shepherd,
Deputy Project Scientist of the Global Precipitation Measurement
Mission at NASA's Goddard Space Flight Center, Greenbelt, Md. and co-
author of a paper that appeared in the May 2005 issue of Bulletin of
the American Meteorological Society.
"Recent U.S. Climate Change Science Program (CCSP) and Weather
Research Program (USWRP) documents highlight the need for improved
understanding of how cities affect weather and climate, yet current
climate models don't represent urban areas very well," said Shepherd.
"Our research suggests that, using satellite data and enhanced
models, we will be able to answer several critical questions about
how urbanization may impact climate change 10, 25 or even 100 years
from now."
Shepherd and co-author Menglin Jin, a research scientist at the
University of Maryland-College Park, suggest that satellite-observed
urban information is extremely useful for advancing our ability to
simulate urban effects in climate models. They go on further to
propose that satellite data is the only feasible way to represent the
expanse of global urban surfaces and related changes to the Earth's
surface, vegetation and aerosols.
According to the United Nations Population Division, urban regions
only cover 0.2 percent of Earth's land surface, but contain nearly
half of the world's population. By 2025, 60 percent of the world's
population will live in cities and urban landscapes will likely
expand well beyond 0.2 percent. However, to date, global climate
models (GCMs) and regional climate models (RCMs) do not reflect urban
landscapes, according to the paper's authors.
GCMs and RCMs are models, or complex mathematical computer
simulations of the atmosphere and the oceans, and are the primary
tool for predicting the response of the climate to increases in
carbon dioxide and other greenhouse gases. GCMs and RCMs combine a
model of land surfaces with an atmosphere model through exchanges of
heat fluxes, water and momentum.
What is it about urban areas like New York City, Paris, Tokyo or
Sydney that the paper's authors believe would lend value to climate
models, and subsequently, to climate predictions? According to
scientific studies presented at a recent American Geophysical Union
session organized by the authors, "the construction of buildings,
parking lots, houses, urban areas dramatically change the smoothness
of a surface, thermal conductivity (the ability of a material to
transmit heat), hydraulic conductivity (measure of the ability of
soil to transmit water), albedo (reflectivity off of Earth's
surfaces) emissivity (the ratio of radiation emitted by a body or
surface) and vegetation cover."
As such, urban landscapes change the typical physical processes of
land surfaces, and importantly, also add new and unique
characteristics to land surfaces and atmosphere.
Structures like the Empire State Building in New York City can change
the basic wind flow in and around cities that can alter air quality,
temperature, cloud distribution and precipitation patterns. It is
increasingly evident that such atmospheric changes near cities can be
captured by NASA satellites such as Aqua, Landsat, Terra, and the
Tropical Rainfall Measurement Mission (TRMM). These same urban
structures also alter the land surface and atmospheric conditions as
measured by satellite instruments such as Aqua's and Terra's Moderate
Resolution Imaging Spectroradiometer (MODIS).
The paper's authors believe that the story of satellites and the city
deserves further review, and can be of great value to our
understanding of how our global inclination to be urban dwellers can
also change the climate of our home planet.
"Our goal with this paper and with our research is to raise attention
to the need for including urban lands into climate models, and for
using satellite observations in simulating those urban landscapes in
climate models," said Jin. "It's important for everyone to know that
urbanization affects things we all care about like the amount and
frequency of rainfall or how hot or cold the outdoor temperature may
be."
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