June 1, 2007 A University of Miami geography professor and his colleagues have crafted a Heat Stress Index that will aim to analyze the daily relative effects of weather on human health. The index and its analysis are based upon key variables and formulas which scientists evaluate daily at different locations around the US. The results are averaged and rated on a scale from 1 to 10; where 1 denotes a less stressful and humid day, and 10 expresses a hot day of sultry weather conditions. Researchers hope that the new index will prove beneficial to the public, since heat is the largest weather-related killer in the United States.
Summertime has most of us thinking of barbeques and beach days. But the summer heat can be deadly! On average, about 1,500 people die from heat-related causes in the United States in an average summer -- that's more than tornados, hurricanes, lightning, and floods combined.
"It's very hot, very humid and very sweaty!" "It takes your breath away." "It feels like death!" These are some of the sounds you can hear when walking down the street in the summertime. According to climatologist Larry Kalkstein, Ph.D., summer heat can really be deadly. Dr. Kalkstein says, "As a matter of fact, heat is the largest weather-related killer in the United States by a large margin."
Dr. Kalkstein says the way to alert people of dangerous conditions is the heat index, but it still doesn't tell us much. He says, "It's a combination of temperature and humidity, and that's all it really takes into account." Weather forecasters will say it feels like 100 degrees but that doesn't tell us how dangerous conditions are. Now, Dr. Kalkstein and colleagues have developed a heat stress index.
Dr. Kalkstein described the new index to DBIS. He said, "What the heat stress index does try to look at the relative impact of weather." It includes previous weather conditions, the maximum and minimum temperatures in your area, cloud cover, cooling degree hours, and consecutive days of extreme heat. The idea is the conditions where you live matter. "What's interesting about this is that you can actually measure how people are going to respond to the weather much better than just an absolute index," Dr. Kalkstein said.
Using the formula of 90 degrees in Boston and 90 degrees in Miami, the new index will render different heat stress indexes -- partly because people living in Miami are used to the heat. The index is on a scale of zero to 10. The National Weather Service will test the new heat stress index in 10 U.S. cities this summer. It could become a mainstream tool by next summer if the test goes well. However, Dr. Kalkstein says the index would not benefit travelers as much because it's based on the previous weather conditions in that particular city. So, while the sun can be fun... remember to stay safe, and look out for a new tool to help you.
BACKGROUND: The Heat Stress Index is a new, comprehensive summer index that evaluates daily relative stress for local locations throughout the United States. The HSI could serve as a guidance system for issuing heat warnings, and as a useful research tool for environmental issues.
HOW IT WORKS: The index is based on daily maximum and minimum temperature, cloud cover, cooling degree hours, and consecutive days of extreme heat. Each of these measurements are taken every day, and scientists then figure out the likely range these measurements usually fall into. (For instance, the average high temperature in your area on July 31 could be between 83 and 105, and the low between 65 and 80.) Then they take all the different measurements taken today, rate them and average them, producing a number between 1 and 10. A 1 day is a very unstressfully hot day, with most other days giving you more stress due to heat at your location at that time of year. A 10 day would be awful, making it the worst day to be stressed by heat that year. A daily value of 9.7, for example, would indicate that only 3 percent of days would be more stressful than the present day at the given location during this time of the year. The same weather conditions in Boston and Atlanta will yield different heat stress index values, based on the city's weather history. The same conditions at the same place would also yield different values if they occurred in early June and mid July.
WHY IT'S NEEDED: It's not the heat, it's the humidity. But why does humidity make you hotter? Humidity is the measure of how much moisture is in the air. The hotter the air, the more moisture it can hold. For example, a high relative humidity of 100 percent means that the air is saturated with moisture and can't hold any more. Our bodies rely on the evaporation of moisture from our skin to keep cool. When relative humidity is low, sweat evaporates from the skin very quickly. But when it is high, body sweat does not evaporate as easily, and we feel sticky and hot.
HEALTH RISKS: Overheating can be very dangerous. Heat exhaustion occurs when the body loses fluid and salt through perspiration faster than they can be replaced, causing dizziness. Exercising in hot weather can cause muscle cramps, especially in the legs, because of brief imbalances in body salts. People not used to exercising in heat may experience a quick drop in blood pressure that can lead to fainting. And in some cases, extreme heat can cause body temperature to rise to 105 degrees or higher, causing a heat stroke, with confusion and unconsciousness. Low humidity makes us feel cooler than the actual temperature because our sweat evaporates quickly. But low humidity can cause dry, itchy skin and chapped lips.
Editor's Note: This article is not intended to provide medical advice, diagnosis or treatment.