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 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 600x300-pixel, 227K JPG . Click here for the entire city in a 1600x977-pixel, 1.8 MB JPG .
	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 600x300-pixel, 227K JPG . Click here for the entire city in a 1600x979-pixel, 2 MB JPG .
	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 600x300-pixel, 235K JPG . Click here for the entire city in a 1661x977-pixel, 2 MB JPG .

"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.

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.