What is a heat wave??

A heat wave is a prolonged period of excessively hot weather, which may be accompanied by high humidity. There is no universal definition of a heat wave; the term is relative to the usual weather in the area. Temperatures that people from a hotter climate consider normal can be termed a heat wave in a cooler area if they are outside the normal climate pattern for that area. The term is applied both to routine weather variations and to extraordinary spells of heat which may occur only once a century. Severe heat waves have caused catastrophic crop failures, thousands of deaths from hyperthermia, and widespread power outages due to increased use of air conditioning.

A heat Storm is an extended heat wave. Heat storms occur when the temperature reaches 100F (38C) for three or more consecutive days over a wide area. Some regions of the globe are more susceptible to heat waves than others, such as Mediterranean-type climates with a summer dry spell which becomes much hotter than usual during certain years.

How they occur

In the summer in warm climates, if there is an area of high pressure with little or no rain and clouds, there is nothing to protect the air and ground from being heated excessively. When large high pressure air is trapped, the ground and air will continue to heat and the heat wave will last longer. The position of the jet stream is very important because the air on one side is hot while the other side is cold. Heat waves are far more likely and more severe when you are on the hot side. Sometimes the jet stream does not move far enough to make many areas that normally get hot on the hot side; but sometimes many cold areas are made hot abnormally. Large desert zones and dry areas are more likely to get extreme heat because there is rarely any high cloud cover with very low humidity, making it like a furnace. The direction of the wind is a very important part of the reasons for heat waves, because this pushes hot air towards colder areas if they are going away from the deserts and equator. The higher the force of the wind as well as the distance they travel from the hotter to colder areas generally means hotter weather. Cities also get hotter because they generate heat from the use of power, usually by about 1-2C or so and experience very warm night time minimum temperatures putting further strain on energy demands. Humidity also has a serious effect on how hot it feels but this does not make the actual temperature any hotter.

Effects on health

Prehaps the most well-known heat-related illness is hyperthermia, also known as heat stroke. Heat edema presents as a transient swelling of the hands, feet, and ankles. Heat rash is a rash accompanied by acute inflammation and blocked sweat ducts. The sweat ducts may become dilated and may eventually rupture. Heat rash affects areas of the body covered by tight clothing. Prevention is the best therapy. It is also advised to wear loose-fitting clothing in the heat. The associated itching may be treated with topical or systemic antihistamines. Heat cramps are painful, often severe, involuntary spasms of the large muscle groups used in strenuous exercise. Heat cramps tend to occur after intense exertion. They usually develop in people performing heavy exercise while sweating alot and replenishing fluid loss with non-electrolyte containing water. Rehydration with salt-containing fluids provides rapid relief. Patients with mild cramps can be given oral .2% salt solutions, while those with severe cramps require IV isotonic fluids. The many sport drinks on the market are a good source of electrolytes and are readily accessible. Heat exhaustion is considered by experts to be the forerunner of heat stroke. It may even resemble heat stroke, with the difference being that the neurological function remains intact. Heat exhaustion is marked by excessive dehydration and electrolyte depletion. Symptoms may include headache, nausea, and vomiting, dizziness, tachycardia, malaise, and myalgia. Most patients will require fluid replacement with IV isotonic fluids at first. The salt content is adjusted as necessary once the electrolyte levels are known. After discharge from the hospital, patients are instructed to rest, drink plenty of fluids for 2-3 hours, and avoid the heat for several days. If this advice is not followed it may then lead to heat stroke. One public health measure taken during heat waves is the setting-up of air-conditioned public cooling centers. Heat waves are the most lethal type of weather phenomenon, overall. Between 1992 and 2001, deaths from excessive heat in the United States numbered 2,190, compared with 880 deaths from floods and 150 from hurricanes. Heat waves often lead to electricity spikes due to increased air conditioning use, which can create power outages, exacerbating the problem. These affect the people, businesses, and hospitals. If a heat wave occurs during a drought, which dries out vegetation, it can contribute to wildfires.