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Coastal Cities
Thu Dec 08, 2005
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Recent trends have shown Americans moving to coastal regions in large numbers. As US coastal cities grow in size and population, urban climatologists are expressing concern over changes in regional weather and climate. Hi, I’m Bryan Yeaton for The Weather Notebook.
High concentrations of buildings, roads, and other artificial surfaces within urban areas retain more heat, which warms temperatures and produces a heat island effect. Urban heat islands cause warm air to rise: a trigger for cloud and precipitation formation.
NASA researchers, using data from the Tropical Rainfall Measuring Mission satellite, have identified changing warm-season rainfall patterns over three years around several American cities The researchers believe rising urban air and converging urban winds enhance local thunderstorm development which drops heavier and more frequent rainfall in and downwind of the cities. The impacts of urbanization in coastal cities may be even greater than inland cities as data from Houston, Texas reveals.
Along a coast, solar heating warms the land more rapidly than the offshore waters, generating an onshore wind-flow pattern known as the sea breeze. Sea breezes also create rising air currents. Researchers think the urban effects enhance sea breeze regimes, and that may further enhance thunderstorm development near coastal cities like Houston.
During the past 60 years, Houston has grown to become the nation’s fourth-largest urban area. NASA researchers found the mean warm-season rainfall rates over the city, as compared to upwind areas, increased 29 percent around the city, and 44 percent.
To rule out non-urban effects on thunderstorm development along the Texas coastline, they analyzed data from seven coastal zones, extending 62 miles inland, and found the only abnormal rainfall pattern occurred over and downwind of Houston. This suggests the impacts of the urban effect is significant.
Thanks to our contributing writer, meteorologist Keith Heidorn. Funding for our Climate Change Series comes from Environmental Defense.
Today's Links
Coastal Cities Turn Up The Heat On Rainfall
http://www.nasa.gov/centers/goddard/news/topstory/2003/0523urbanrainfall.html
Are Cities Changing Local And Global Climates?
http://www.nasa.gov/vision/earth/environment/Changing_Cities.html
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