Heat's health threat to cities may be most problematic in Louisville, Ky.

Louisville, Ky., has finally caught a break.

Following several days of triple-digit temperatures last week, thunderstorms yesterday cooled the air and slaked the thirst of the city on the south bank of the Ohio River. It was a welcome relief for the city's 740,000 residents and the more than 1 million people residing in the metropolitan area.

The recent heat wave wilted Kentucky's famed bluegrass across lawns and parks, and Churchill Downs, home of the Kentucky Derby, canceled a horse race for the first time due to high temperatures. "I've been down here for 25 years now, and I don't recall this many days in a row with the heat going up into triple digits," said Dave Langdon, spokesman for the Louisville Metro Department of Public Health and Wellness.

Throughout the heat-afflicted region, spanning much of the continental United States, pavement buckled, mailboxes tipped over and temperature records broke. At Ronald Reagan National Airport near Washington, D.C., a U.S. Airways flight to Charleston, S.C., was delayed Friday because the plane sank too far into the heat-softened asphalt. Power systems in several states strained as air conditioners switched on and utilities struggled to restore power to areas already darkened by severe storms last month (see related story).

But the cool reprieve may be fleeting, as severe thunderstorms set in across the country. This cycle of jumping out of the frying pan and into the flood may repeat itself over the long term as milder summers become fewer and further between under a warming climate. Among the many cities involved, Louisville may suffer the most.

The city is poised to endure the most heat-related deaths of any city in the United States, according to a study the Natural Resources Defense Council (NRDC) released in May. More than 150,000 Americans will die from extreme heat by the end of the century, the report found, and 19,000 may come from Louisville.

The report also estimates that 39 Louisville residents die annually from extreme heat but says that number will rise to 270 by midcentury due to climate change, further rising to 376 by 2100. Langdon said there have not been any casualties in the city attributed to the heat so far this year, but researchers say the true toll may not be known for years, since excess heat plays into a variety of health conditions and is difficult to isolate.

Shade is hard to come by


So why can't Louisville residents cool off? Part of the reason is that they don't have enough shade. The city is among the few that do not have a comprehensive tree ordinance to protect existing trees and plant new ones. Over the past 50 years, trees were lost not to the city's namesake baseball bats, but to storms and development, as well as aging and attrition.

A University of Louisville assessment found that trees cover a paltry 27 percent of Jefferson County, which includes Louisville, and 8 percent of the downtown area. Atlanta, on the other hand, has a tree canopy that shades more than 50 percent of the city with 20 to 30 percent coverage in its downtown. Nearby cities, like Cincinnati and Nashville, Tenn., have similar urban foliage levels.

In addition, Louisville, like most urban areas, experiences a heat island effect, where temperatures in the city are regularly higher than surrounding rural areas. However, scientists found that Louisville experiences the strongest heat island effect in the United States, partly because of the shade shortage.

Researchers have long understood that cities warm faster than their surrounding environments. Dark asphalt and concrete absorb heat and tall buildings help trap it, and as cities expand, cooling vegetation is lost to sidewalks and roads. "Not only does that make the city warmer, it appears to be amplifying global-scale warming," said Brian Stone Jr., an associate professor of city and regional planning at the Georgia Institute of Technology.

Stone, who published a book last month titled "The City and the Coming Climate: Climate Change in the Places We Live," developed an index that evaluates temperatures in cities and compares them to their more rural surroundings rather than simply measuring the absolute temperature increase. The idea is to get a regional baseline so scientists and planners can figure out how much warming comes from global climate change and how much comes from variables in the city itself. Using this measurement, scientists found that Louisville induces more warming than any other indexed city in the United States. "Louisville is a real outlier," Stone said.

A hidden health issue

This accelerated warming poses disastrous consequences for public health. According to the Centers for Disease Control and Prevention, roughly 400 people die each year from heat exposure alone, while many more suffer from heart and lung complications exacerbated by heat, making it one of the deadliest health threats.

However, Larry Kalkstein, a climatology professor at the University of Miami and a co-author of the NRDC report, explained that there is more to heat health impacts than how high you push the mercury. "The thing that we forget about this is that it's not just the intensity of heat, but the variability of the weather," he said. "People don't know how to react to heat waves in many cases where it's rare ... fewer people die in Phoenix and south Florida than Toronto."

Though cities like Phoenix may experience hotter temperatures, their denizens are more conditioned to the weather and have the resources and foreknowledge to cope. Kalkstein noted that other variables also affect risks for heat deaths in cities, like the proportion of elderly residents and emergency response systems to handle extreme weather.

To prevent deaths, Kalkstein suggested officials concentrate on educating the public. "Generally, we have found people do not consider themselves vulnerable to the heat," he said. "Most of those people are wrong." Anyone can suffer from heat stroke or exhaustion, he noted, including young, active people who consider themselves acclimated to the temperature. Nonetheless, the very young, the elderly, the obese and those on medication face greater risks.

"The effects of overexposure to the heat can occur suddenly, and one of the symptoms is impaired judgment, so you may be in trouble and not know it," said Langdon from the public health department. To help combat this problem, Langdon said, Louisville is offering public air-conditioned spaces for residents to cool down and day shelters for the homeless.

He also noted that social isolation is a factor in many heat-related deaths, since the elderly, the immobile and shut-ins might suffer without anyone knowing or coming to their aid. Here, Louisville may have an advantage. "Louisville thinks of itself as a compassionate city," Langdon said. "Louisville is a city that reaches out to its fellow citizens."

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