Heat Waves (2): Heat and Humans

The long spell of hot days broke in Denver, and my garden is starting to look happier. Still, I want to write one more about heat waves now. (At the bottom, I have a couple of off topic question. One's for teachers, one is for gardeners?)

From a human health point of view, heat waves are often listed as an urban problem. There have been a number of events in the past few years that have brought this message to the forefront. One of the most prominent heat waves was the sustained heat in Europe in 2003, which has been associated with more than 20,000 deaths. (Here is an old USA Today link to the impact in Paris.) The heat wave in Chicago in 1995 motivated much activity in the United States to develop better heat-health warning systems. (Here are a couple of articles from the Bulletin of the American Meteorology Society. Tom Karl and Richard Knight (Chicago Heat Wave) Larry Kalkstein et al. Philadelphia Heat Health Warning System)

In the previous blog the role of environmental , geographical and population information (Figure 1). It would seem to be a simple thing to calculate "when it is hot;" that is, the environmental information.




Figure 1. A schematic of the types of information needed in order to evaluate and respond to environmental heat threats.

Looking at the recent period of prolonged heat in Denver, however, it was not a period of with high human health impact. Perhaps this is because it was well reported, and Denver is an area used to summer heat. Examination of past heat waves give more information.

First, if you look at the Karl and Knight paper referenced above, they use a simple formula for identifying a heat wave. That definition is the nighttime minimum for three days. And, in fact, sustained high nighttime minima are one of the best predictors of human heat health threats. This is an indicator of both the inability of buildings to cool down and people to cool down. In Colorado, where it is dry and often not so cloudy, it continued to cool down at night.

Looking further, a hot spell in April or May in, say, Saint Louis, has a much greater health impact than the same or higher temperatures in August. Hence, there is an element of preparedness, acclimation, or expectation that has a large impact. 95 degrees F in Montreal or Paris is much more dangerous than 95 degrees F in Houston. 95 degrees F in a city where air conditioning is uncommon is more dangerous than where air conditioning is common. Hence the calculation of environmental heat that will be a health threat is far more difficult than calculating the temperature, or even a temperature-humidity combination, like the heat stress index.

(BTW, is you are in an enclosed building, blowing a fan at yourself, a stream of hot air, can make things worse because it dehydrates you faster. Remember that!)

The situation mentioned above is derived primarily from cities, which has been where the greatest public health impact is found. This threat is stongly correlated with chronic day and night high temperatures as well as some measure of "preparedness." There is another type of heat threat which is associated with people who are exercising or who are exposed to extremely high heat. In this case there is a temperature, some place around 105 degrees F, where the mortality rate jumps up. Here is a paper by Sam Keim who works in an emergency room in Arizona.

The human heat health problem indicates the complexity that is realized when trying to address environmental conditions, their impact on health, and how to address those impacts. Next time a little about heat waves and climate change.

Remember my gardening and teaching question below.

r

Some previous heat wave blogs

Hot in Denver: Heat Waves (1)

Letter from India
Heat, Flood, and Fires
Records and Patterns


1) Gardening: I know that some of you are avid gardeners of the organic flavor. I have been trying to find out information about irrigation systems. In particular, have you read anything about PVC pipe and chemicals placed in water or soil?

2) Teaching: I have been contacted by several people who are using my notes to teach climate change across disciplines. Some have expressed interest in starting a "community." If you teach or know of other courses that are teaching problem solving in climate change, let me know. (rbrood@umich.edu)