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Heat Waves

Heat Waves extended definition

Heat waves are extended periods of unusually hot weather that affect human and animal health as well as energy use.

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Why do I care?  Heat waves can potentially worsen drought conditions, which can be devastating to growers and crops.  The increased temperatures will cause the crops to dry out through evaporation and decrease the available food supply. Heat waves can also impact energy demands on consumers and leave some populations without a cooling mechanism because of the increased use of air conditioners. The severe heat stress can affect animal health as well as human health and potentially lead to an increase in human and animal mortality if cool areas are not available.

Heat waves prerequisites

I should already be familiar with: Drought, Pressure

Heat Waves body


 

Heat waves, particularly those with excessive humidity, can accompany and possibly worsen the effects of drought. Heat waves are prolonged periods of very hot weather, with temperatures at least 9 degrees Fahrenheit greater than the average daily maximum. They usually have the most impacts during summer months when normal temperatures are already high.  They occur when a ridge of high pressure sits over a region for an extended period of time, bringing down dry, hot air to the ground.   As the air sinks, it warms and compresses and is very hot by the time it reaches the surface. This hot air quickly heats up the ground, which raises the air temperature well in excess of the average daily maximum.  Since the center of high pressure areas are usually cloud-free, the direct sunlight further raises daytime temperatures.

If humidity is high, temperatures do not cool much at night.  Nighttime heat greatly contributes to heat stress because the body has no relief from the oppressive conditions.  Stress continues to build as the hot conditions continue.

Heat waves create special danger to the elderly and to young children as well as some animals. In order to cool down the body, a person will sweat to release heat and provide a source of moisture for evaporation, which cools the skin surface. If the humidity is high, sweating does not cause much cooling because the air already contains a lot of moisture and evaporation is slow.  The elderly and young children heat up faster because their bodies are less able to regulate their internal temperatures and that makes them particularly vulnerable to prolonged heat spells.

In heat waves, it is important for people to stay cool.   Many cities now have local air-conditioned centers where people can go to cool off as relief from the heat.   Some police stations will also check on the elderly to make sure they are comfortable with the increased temperatures outside in order to minimize heat-related deaths.  If you are in a rural area, it is important to get to areas with air conditioning like a shopping mall or movie theater or a friend's house to avoid putting yourself in danger.  If you need to work outside, you should take frequent breaks in cool areas and drink a lot of water to prevent dehydration.  If you stop sweating in hot conditions, seek immediate medical attention because your body may be overheating, leading to heat exhaustion and even death.

1930s Dust Storm

Figure A: 1930s Dust Storm
Image from NOAA

In rare instances power outages are possible because of the increased use of air conditioners, especially in regions where air conditioning throughout the year is usually unnecessary. The added use puts stress on the electrical utilities because everyone turns on maximum air conditioning at the same time.  The increased demand can cause substations to overheat and shut down, cutting off air conditioning to thousands of people at the time they need it most. Home air conditioners are also at risk of shutting down due to hot temperatures, usually above 100°F, over many days with increased usage.

Heat waves and drought often go hand in hand.  Because of the persistent ridge and sinking air, clouds do not form to offer relief with precipitation. The heat waves only add to the drought conditions by greatly increasing evaporation and stress on plants and water supplies. Heat waves, however, usually only last for a couple of days, whereas drought conditions can last for years.

When heat waves occur in severe drought conditions, you can see an increase in the number of wildfires and dust storms that are observed.  Under continuous drought conditions, the soil dries up and the ground begins to crack. When this happens, the soil breaks apart and becomes loose. A heat wave only enhances the drying up of the land. Strong winds can pick up the loose soil and blow it for hundreds of miles, reducing soil fertility drastically.  In the 1930s, the “Dust Bowl” occurred in this manner. Persistent drought conditions hovered over the Midwest because of the lessened amount of precipitation for many years. Persistent ridges also lingered over this area. This allowed very hot, dry air to descend onto the Midwest and suck up any moisture that was left in the plants near the ground. This dried up the plants faster and the soil had nothing to keep it together and the wind blew the soil away in huge masses.  Ultimately, this caused massive migration of farmers away from the depleted areas and severe hardship for those who stayed.

Heatwaves relation to health

How does this relate to public health?

One recent model suggests that by year 2059, the Southeast can expect a 2-3°F increase in heat wave intensity and 1-2 more days per heat wave. Similarly, North Carolina is predicted to see a 2.79°F increase in heat wave intensity and 2.63 more days per heat wave.1

“In heat waves, it is important for people to stay cool. Many cities now have local air-conditioned centers where people can go to cool off as relief from the heat. Some police stations will also check on the elderly to make sure they are comfortable with the increased temperatures outside in order to minimize heat-related deaths.

In North Carolina, agricultural workers and young athletes who spend several hours a day outside are especially vulnerable to heat-related illness during heat waves. In fact, from 1992 to 2006, the annualized rate for reported heat-related deaths among crop workers in the U.S. was highest in North Carolina at 2.36 deaths per 100,000 workers.2

If you are in a rural area, it is important to get to areas with air conditioning like a shopping mall or movie theater or a friend's house to avoid putting yourself in danger. If you need to work outside, you should take frequent breaks in cool areas and drink a lot of water to prevent dehydration.

If you stop sweating in hot conditions, experience heat cramps or faint, seek immediate medical attention because your body may be overheating, leading to heat stroke and even death.”

Rising average temperatures and more frequent and more intense heat waves due to climate change are affecting human health in several ways. Most directly, warmer average temperatures and more extreme temperatures put more people at risk for heat-related death and disease, such as heat stroke and dehydration.3 For example, in North Carolina, the number of heat-related visits to the emergency department increases by 15.8 for every 1°F increase in temperature from 98°F to 100°F.4

Figure B
Image from Centers for Disease Control and Prevention

Older adults and young children are vulnerable to heat-related illnesses. However, over the past two summers, North Carolina has seen the greatest number of heat-related visits to the emergency department among men ages 25-64.5,6

Figure C: Heat-related emergency department visits by age group in 2011 Figure D: Heat-related emergency department visits by age group in 2012

Images from North Carolina Division of public health

In addition, heat stress increases the risk for other diseases, especially respiratory death. In the U.S., severe heat events account for more deaths than all other extreme weather-related events combined each year. With increasing temperatures due to climate change, summertime heat-related deaths are expected to increase significantly, while wintertime deaths are expected to decrease slightly.3


1Gao, Y., et al. (2012). Projected changes of extreme weather events in the eastern United States based on a high resolution climate modeling system. Environmental Research Letters,7(4), 044025.

2Luginbuhl, RC; Jackson LL; Castillo DN; Loringer KA. heat-related deaths among crop workers --- United States, 1992—2006. MMWR 2008;57(24);649-653. <http://www.cdc.gov/mmwr/PDF/wk/mm5724.pdf> Accessed November 17, 2012.

3Portier CJ, et al. 2010. A human health perspective on climate change: a report outlining the research needs on the human health effects of climate change. Research Triangle Park, NC: Environmental Health Perspectives/National Institute of Environmental Health Sciences. doi:10.1289/ehp.1002272 <www.niehs.nih.gov/climatereport> Accessed November 17, 2012.

4Rhea, S; et al. 2012. Using near real-time morbidity data to identify heat-related illness prevention strategies in North Carolina. Journal of Community Health 37:495-500. DOI 10.1007/s10900-011-9469-0.

5North Carolina Division of Public Health, Occupational and Environmental Epidemiology. The 2011 North Carolina heat report. July 2011. <http://publichealth.nc.gov/chronicdiseaseandinjury/doc/HeatReport-13-2011.pdf> Accessed November 17, 2012.

6North Carolina Division of Public Health, Occupational and Environmental Epidemiology. The 2012 North Carolina heat report. <http://publichealth.nc.gov/chronicdiseaseandinjury/doc/HeatReport20-2012.pdf> Accessed November 17, 2012.


Last modified date: Thursday, August 1, 2013 - 1:38pm