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A heat wave is a combination of temperature and humidity for a prolonged period. Generally, temperatures is more above the average high temperature for the region.It is an extended period of very high summer temperture with the potential to adversely affect communities. High temperture are often accompanied by high humidity, that the body cannot tolerate are defined as extreme heat. A heat wave is a very dangerous situation and major threat to lives. According to the World Meteorlogical Organisation (WMO), 1998 was the hottest year on
record. Over the last 25 years the average global temperature rose by 1 degree Fahrenheit, or 0.6 degrees Celsius. The Intergovernmental Panel on Climat Change (IPCC) 's projected rise in temperature for this century is a global average, but the temperature is expected to rise more over land, where people live,than over sea.As temperatures continue to climb,the toll of heat waves in individual countries could jump from the thousands to the tens of thousands.The World Meteorological Organization estimates that the number of heat-related fatalities could double in less than 20 years. Already we are seeing evidence of more frequent heat waves. In India, death tolls from heat that were recorded over an entire summer some 10 years ago are now occurring in just one week. Some of the increase is due to urbanization, a trend that is expected to
continue for the foreseeable future.Heatwave is also one of the major disaster for many countries for live lost like other natural disasters. Many heat related deaths go unreported because they are taken to be the consequensces of the exisitng ailments.In Orissa,heat wave caused 2042 deaths in 1998 and more than 1200 deaths in 2002 southern India. Temperatures have risen to between 45 and 50 degrees Celsius (113 to 122 degrees Fahrenheit), nearly 10 degrees above the normal level, with the highest reading of 50 degrees reported. Apart from death, every day more and more people have been admitted with suffering sunstroke and severe dehydration, with vomiting and high fever.

Some of the definition related to Heat Wave/ stroke

Heat Index
A number in degrees Fahrenheit (F)that tells how hot it really feels when relative humidity is added to the actual air temperature. Exposure to full sunshine can increase the heat index by 15 degrees.

Heat Cramps
Heat cramps are muscular pains and spasms due to heavy exertion.Although heat cramps are the least severe, they are often the first signal that the body is having trouble with the heat.

Heat Exhaustion
Heat exhaustion typically occurs when people exercise heavily or work in a hot atmosphere or direct sun , humid place where body fluids are lost through heavy sweating. Blood flow to the skin increases, causing blood flow to decrease to the vital organs. This results in a form of mild shock. If not treated, the victim's condition will worsen. Body temperature will keep rising and the victim may suffer heat stroke.

Heat stroke / Sun stroke
Heat stroke is life-threatening.The victim's temperature control system,which produces sweating to cool the body, stops working. The body temperature can rise so high that brain damage and death may result if the body is not cooled quickly.

Impacts & Effects of Heat Wave
A heat wave is an extended interval of abnormally hot and usually humid weather, usually lasting from a few days to over a week.
Human Being
In many parts of world , every summer , thousands of people suffer from heat stress when their bodies aboserb more heat than they can expel. Depletion of salt and electrolyte in the body may cause heat cramp, hard work under the direct sun may lead to heat exhaustion.Usually ,it is the cummulative ewffect of hot days without the relief of cool nights and exposure to exhaustion.
Heat can kill by pushing the human body beyond its limits. Under normal conditions, the body's internal thermostat produces perspiration that evaporates and cools the body. However, in extreme heat and high humidity, evaporation is slowed and the body must work extra hard to maintain a normal temperature. Elderly people, young children, and those who are sick or overweight are more likely to become victims of extreme heat. Because men sweat more than women, they are more susceptible to heat illness because they become more quickly dehydrated. People living in urban areas may be at greater risk from the effects of a prolonged heat wave than people living in rural regions. While people in rural areas generally get some relief from the heat when temperatures fall at night,urban areas stay warmer around the clock. Air pollution, which usually is worse in cities than in the
countryside, can also exacerbate the health-damaging effects of high temperatures by further stressing the body's respiratory and circulatory systems. In addition, asphalt and concrete store heat longer and gradually releases heat at night, which produces significantly higher nighttime temperatures in urban areas known as the "urban heat island effect." Heat wave caused unfold misery to people all over the world . In 1198 , about 1500 people were died in China and in 1997 about 2000 people fell to heat wave in Greece. Similalry in Inida the heat wave took 3028 lives in the year 1998 and more than 2000 people in the year 2002. Heat wave also caused death of wild life such as monekies were died in UP and in most of the zoos in India.

Like human beings, animals too suffer , particularly when they are left in the direct sun and they do not get adequate water. Domestic animals and poultry birds are particulary vulnerable to heat wave.

Agriculture and Crop
Heat waves also damage plants, crops and vegetables. When searing winds blow and the temperture rises to around 450 C , exotic plants perish. When temperture exceeds 450 C for a number of days even the traditional species suffer, particulalry if they do not receive moisture regulalry. In the grazing filed not a single blade of grass is available for the cattle.

During heat wave , the railway lines can expand to the point where they buckle and caused derailment of train. Road damages can also occur with bitumen melting and concrete expanding and having cracks. Even bridges may have similar type of damages.

During hot summer water consuption incereases drastically and often causing shortage of drinking water. Lack of water in most of the wells , pond, tubewell and other bodies during hot summer seasons, which has an advereffect on human being and animal population. Under normal circumstances, humans maintain a body temperature around 98.6 degrees Fahrenheit. When subject to extreme heat, the body attempts to maintain this ideal temperature by varying blood circulation and perspiring. When the internal body temperature rises above 104 degrees Fahrenheit, vital organs are at risk. If the body temperature is not brought down, death follows. The threshold ambient temperature at which more people are at risk for heat-related health problems varies greatly by location. In general, when summer temperatures
range 10 degrees Fahrenheit or more above the norm, incidences of heat-related illness increase dramatically. High humidity compounds the effects of high heat by reducing evaporation, rendering perspiration a less-effective cooling mechanism. When excessive heat prevails for more than two consecutive days, the risk of heat sickness and death escalates. Health and social services may be overwhelmed.

Heat Wave conditions can result in physiological strain, which could even result in death. Orissa, Andhra Pradesh and Tamil Nadu have experienced sever heat wave conditions since last few years during April to mid June and nearly 5,000 people died of heat stroke.

Signs & Symptoms of Heat Wave

Heat Exhaustion
Cool, moist, pale, or flushed skin; heavy sweating; headache; nausea or vomiting; dizziness; and exhaustion. Body temperature may be normal, or is likely to be rising.
Heat Strokes
Hot, red skin; changes in consciousness; rapid, weak pulse; and rapid, shallow breathing. Body temperature can be very high -sometimes as high as 1050 F. If the person was sweating from heavy work or exercise, skin may be wet; otherwise, it will feel dry.
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