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  • Steven Shepard
    Study Confirms That Urban Heat Islands Cause Downwind Rain Residents of flooded rural areas near San Antonio, Texas, have one more reason to complain about
    Message 1 of 1 , Jul 10, 2002
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      Study Confirms That Urban Heat Islands Cause Downwind Rain

      Residents of flooded rural areas near San Antonio, Texas, have one
      more reason to complain about their city-dwelling neighbors: a new
      study shows that the heat generated by cities helps produce
      rainstorms downwind from cities. The study, led by the U.S. National
      Aeronautics and Space Administration's Goddard Space Flight Center,
      used a rain-measuring satellite to verify similar results obtained
      in previous ground-based studies. The satellite data demonstrated
      that major cities -- including Nashville, Atlanta, Dallas, and, yes,
      San Antonio -- increased downwind rainfall by about 28 percent
      within 18 to 36 miles from the cities. In some cities, the downwind
      area rainfall increased as much as 51 percent. On average, maximum
      rainfall rates in downwind regions exceeded the maximum values in
      upwind regions by up to 116 percent.

      Cities basically act as giant solar collectors: during summer
      months, the dark roofs, concrete, asphalt, and other surfaces in the
      cities absorb a large amount of heat. The resulting "heat island"
      effect can boost urban temperatures by 5 to 9 degrees Fahrenheit.
      During the warmer months, the added heat creates wind circulations
      and rising air that can produce clouds or enhance existing ones.
      Under the right conditions, these clouds can evolve into rain-
      producers or storms. See the Goddard Flight Center press release at:
      <http://www.gsfc.nasa.gov/topstory/20020613urbanrain.html>.

      Urban heat islands have long been of concern, since they drive up
      the use of air conditioners, increase ozone levels, and exacerbate
      health problems. In fact, the city of Toronto hosted the North
      American Urban Heat Island Summit in early May. The presentations
      from that summit are now posted on the City of Toronto Web site at:
      <http://www.city.toronto.on.ca/taf/agenda.htm>.


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