Nov 20, 1998

Cities Getting Ready for Next Heat Wave

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Cities getting ready
for next heat wave


Results applied from
Urban Heat Island Pilot Project


November 20, 1998: As the first chills of autumn erase the memories of this summer's heat wave, three cities are starting to apply lessons from sweltering portraits painted by a NASA-led team of Earth scientists.

Salt Lake City is figuring out how to keep the air clean for the 2002 Summer Olympics, and Baton Rouge and Sacramento are planning where to plant trees.

Right: Sacramento displays a little of everything, from blistering railyards to the cool California River, in visible and thermal infrared images. Detailed images are available below. Credits for all photos: NASA/Marshall Space Flight Center.

These new efforts come as a result of data from the Urban Heat Island Pilot Project (UHIPP) which coordinated observations by ground teams with airborne and satellite sensors and cameras of the three "pilot cities:" Baton Rouge, Louisiana, May 18; Sacramento, California, June 29; and Salt Lake City, Utah, July 13 and Sept. 15 (a second flight because of instrument problems on the first flight). Several other U.S. cities participated through ground-based and satellite observations. Atlanta was studied in May 1997.

Teaming with NASA's Marshall Space Flight Center in the pilot project were the U.S. Environmental Protection Agency (EPA), the U.S. Department of Energy, the Lawrence Berkeley National Laboratory, Baton Rouge Green, the Sacramento Tree Foundation, Tree Utah, and the Utah State Energy Services Department.

The ultimate objective of the EPA, UHIPP's principal funding agency, is improving air quality, specifically by reducing ozone. The overall goal of this project is finding ways to cool the city and thereby reduce ozone pollution problems.

Although most science projects take months to complete, and even longer to produce results, the UHIPP team is pushing to get the data out to city planners by year's end.

Starting this month, NASA and the EPA are working with the Pilot Cities to develop "Action Plans" that will: 1) categorize land use across the city; 2) estimate the areas of maximum potential for reflective surfaces and urban afforestation; 3) identify which organizations within the city or a given community would be appropriate in helping to implement the mitigation measures; and 4) outline and prioritize policy levers and potential programs that offer the largest cooling potential at the least cost.

"This is not a research project," said the study's lead investigator, Dr. Jeff Luvall of Marshall Space Flight Center's Global Hydrology and Climate Center. "We want to get the data out to city planners as soon as possible." The raw data sets will be about 2 to 3 gigabytes per city. That will swell when the data are fully calibrated to correct for atmospheric interference and apply laboratory optical bench calibrations to the instruments.


The basic concept behind UHIPP can be felt on a hot day when you drive from city canyons to wooded areas: it gets cooler.

"While UHIPP is quite complex," Luvall explained, "at its core is the fact that the evaporation of water absorbs a lot of heat. Plants, and trees in particular, evaporate large amounts of water from their leaves. The energy required to evaporate water is taken from the air and from the sunlight intercepted by the leaves, thus cooling the air. Trees are also very effective in shading the ground, thus preventing the heating of the surface by sunlight."

On the other hand, asphalt, concrete, and other manmade materials are very effective at absorbing light and reradiating it as infrared radiation that raises the temperature of the air. In turn, that makes air conditioning systems work harder, even after sunset. As a result, utility bills go up and heat stress as a result of increased heat over the city can affect human health.

Atop all that, depending on weather conditions, the hot air will form a dome or bubble over the city which is several degrees warmer that the surrounding countryside.

Feeling cooler is a nice feeling, but city planners need hard data to help justify changes in how things are done. Thus, UHIPP is providing a series of demonstrations.



The bird's eye view


While weather satellites and ground observers played important roles in UHIPP, the key instruments were the Advanced Thermal and Land Applications Sensor (ATLAS) and a 23x23 cm (9x9 in) film camera carried aloft by a NASA Lear 23 jet (above) operating from Stennis Space Center. ATLAS - basically the same as the main camera aboard the Galileo spacecraft - sees in 15 distinct wavelengths. It readily shows concrete and asphalt glowing bright in thermal infrared, while trees and other vegetation are darker because the sun's energy is being dissipated mostly through the evaporation of water from their leaves. The film camera provided visible images to match hot and cold spots with known objects on the ground. Links to .



A UHIPP sampler

The images below are visible (left) and thermal infrared (right) sections from the larger images covering each city. Because each image has not been calibrated, absolute temperatures will change after calibration, but the relative temperature differences between surface types will not.



Baton Rouge, La.:The yellow and red areas are hot, and generally correspond with roads and buildings; blue and green areas are cool and indicate water and vegetation. The bright red areas in this image are about 65 deg. C (149 deg. F); dark green and blue areas are around 25 deg. C (77 deg. F). The solid blue swatch of color flowing down the left side is the Mississippi River. Links to . Click here for the entire city in a .


Sacramento, Calif.: The white areas, mostly rooftops, are about 122 deg. C (140 deg. F) and the dark areas are approximately 29-36 deg. C (85-96 deg. F). The hottest spots are buildings, seen as white rectangles of various sizes. Sacramento's rail yard is the orange area east of the Sacramento River, which flows from top to bottom. In the complete image, the state capitol is the red spot in the green rectangle to the right center of the river. Links to . Click here for the entire city in a .


Salt lake City, Utah: Again, the yellow and red areas are hot and generally correspond with roads and buildings; blue and green areas are cool and indicate water and vegetation. The white areas are about 71 deg. C (160 deg. F); blue and green areas are approximately 29-36 deg. C (85-96 deg. F). The complete image spans Salt Lake City from about 300 West Street on the left edge of the image, to the foothills of the Wasatch Mountains on the eastern edge. Links to . Click here for the entire city in a .


"We're starting to develop sample data sets, even though they're not fully calibrated, to get the feel for how to handle it," Luvall said. The data packages will include public domain software and low-cost geographic information systems to help city planners map the data onto specific parts of their cities.

"The sooner we can get the data out to the people, the quicker they can learn how to deal with it when the calibrated sets are available," Luvall said.

Already, the preliminary results are having an effect.


Salt Lake City is using the early results to help plan sites for the 2002 Winter Olympic Games and develop strategies to reduce ground-level ozone concentrations in the Salt Lake City valley. Not to be confused with the "good" ozone layer protecting Earth from ultraviolet rays, ground-level ozone is a powerful and dangerous respiratory irritant found in cities during the summer's hottest months.


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Web Links
More on the Urban Heat Island Project
  • Atlanta, Georgia, May 1997
  • Baton Rouge, Louisiana, May 18, 1998
  • Sacramento, California. June 29, 1998.
  • Salt Lake City, Utah. July 13, 1998.
  • Project Atlanta
  • Global Hydrology and Climate Center
  • Islands in the (Air) Stream (May 1, 1998)
  • Newsweek Article: Blue Skies Ahead - Hot Ways to Cool Down Our Cities

In Sacramento and Baton Rouge, city planners and tree planting organizations are using the study to focus their tree-planting programs.

"We are helping the cities incorporate the study into their urban planning," said Maury Estes, an urban planner with the Universities Space Research Association and a part of the science team at NASA/Marshall. "By choosing strategic areas in which to plant trees and by encouraging the use of light-colored, reflective building material, we think that the cities can be cooled."

Meanwhile, UHIPP data are being used by Luvall and his colleagues, and by scientists at the Lawrence Berkeley National Laboratory, to produce computer models so planners from other cities can better predict the heat island effect for their cities, and then plan remedies.


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Author: Dave Dooling
Curator: Bryan Walls
NASA Official: Gregory S. Wilson