Is the high temperature heat wave a wave?

In midsummer, Tianjin, Jinan, Zhengzhou, Xi, Shijiazhuang and the middle and lower reaches of the Yangtze River are under the control of the western Pacific subtropical high, which is the hardest hit area of summer heat wave in China. [1] In July and August after the rainy season, there will be 20 to 30 days of hot weather in general years, and the number of hot days in short rainy season can exceed 40 days. In recent 50 years, the average number of high temperature days in China has decreased at first and then increased. From the 1950s to the early 1980s, the days of high temperature showed a decreasing trend, and began to show an obvious increasing trend in the early 1980s. The number of high temperature days in northwest and north China is increasing linearly, especially in south China.

High temperature is also a common meteorological disaster, which has a certain impact on people's daily life and health as well as all sectors of the national economy. High temperature and heat wave make people uncomfortable, work efficiency is low, and the incidence of heatstroke, intestinal diseases, cardiovascular and cerebrovascular diseases increases; The demand for water and electricity for heatstroke prevention and cooling has soared, resulting in tight water and electricity supply and frequent failures. High temperature aggravated soil water evaporation and crop transpiration. When high temperature and little rain occur at the same time, soil moisture is seriously lost, which accelerates the development of drought and has a great impact on agricultural production. Continuous high temperature and little rain are also easy to cause fires, and forest fires will destroy the ecological environment. [2] In addition, tourism, transportation, construction and other industries will also be affected to varying degrees, but the high-temperature heat wave will also bring business opportunities to some manufacturers and businesses that produce and sell heatstroke prevention and cooling supplies and equipment.

Introduction of high temperature heat wave standard

The standard of high temperature heat wave is mainly based on the influence or harm degree of high temperature on human body.

The disaster of high temperature and heat wave is influenced by geography, society and economy. Different countries and regions in the world use different methods to study high-temperature heat waves, and the standards of high-temperature heat waves are also very different. At present, there is no unified and clear standard of high temperature heat wave in the world. [3]

China high temperature heat wave standard

In China, the highest daily temperature reaches or exceeds 35℃, which is called high temperature, and the high temperature weather process lasting for several days (more than 3 days) is called high temperature heat wave (or high temperature heat wave). Due to the frequent occurrence of high temperature and heat waves in recent years, the disasters caused by high temperature are becoming more and more serious. To this end, China's meteorological departments have specially formulated high-temperature warning signals to defend against high-temperature weather.

The standard of the influence of high temperature on other organisms can be formulated according to the temperature value when it reaches the hazard.

Foreign high temperature heat wave standard

WMO (World Meteorological Organization) suggests that the standard of high-temperature heat wave is: the maximum daily temperature is higher than 32℃ and lasts for more than 3 days.

According to the Royal Dutch Meteorological Institute, the daily maximum temperature is higher than 25℃ and lasts for more than 5 days, of which the maximum temperature is higher than 30℃ for at least 3 days.

The meteorological departments of the United States, Canada, Israel and other countries issued high-temperature warning according to the thermal index (also known as apparent temperature) that comprehensively considered the influence of temperature and relative humidity. For example, the standard for issuing high-temperature warning in the United States is to issue a high-temperature warning when the daytime thermal index exceeds 40.5℃ for two consecutive days or the predicted thermal index exceeds 46.5℃ at any time.

German scientists have worked out the human body temperature index according to the human body heat balance model. For example, when the physiological equivalent temperature (PET) of human body exceeds 4 1℃, the thermal mortality rate increases significantly. Therefore, the physiological equivalent temperature (PET) of human body is greater than 4 1℃ as the early warning standard of high temperature heat wave.

Brief introduction of high temperature heat wave types

Because the human body's feeling of hot and cold depends not only on temperature, but also on air humidity, wind speed, solar radiation and so on. Therefore, the high temperature weather under different meteorological conditions also has its corresponding characteristics. There are usually two types: dry-hot type and muggy type.

Dry heat and high temperature

High temperature weather with extremely high temperature, strong solar radiation and low air humidity is called dry heat and high temperature. In summer, northern China such as Tianjin, Shijiazhuang, Jinan, Zhengzhou, Xi, Turpan and other places often appear.

A sultry high temperature

Because of the rich water vapor and high air humidity in summer, when the temperature is not too high (relatively speaking), people feel sultry, just like in a steamer. Such weather is called sultry and high temperature. Because people like to take a sauna in this weather, it is also called "sauna day". It often appears in Tianjin, Jinan, the middle and lower reaches of the Yangtze River in northern China, and in southern China.

High temperature hazard

High temperature and heat wave make the human body unable to adapt to the environment and exceed the tolerance limit of the human body, leading to the occurrence or aggravation of diseases and even death, and so do animals; At the same time, high temperature and heat wave will also affect the growth and development of plants and reduce crop yield. The high temperature heat wave process will also aggravate the occurrence and development of drought; The rapid increase of water consumption and electricity consumption has a great impact on people's life and production. In addition, high-temperature heat waves often make people fidgety and even lose their minds, which easily leads to public disorder, accidents, casualties, poisoning, fires and other events, which are indirect effects of high-temperature heat waves.

The influence of meteorological conditions in the environment on human body is the result of the comprehensive action of many meteorological factors. For example, people's comfort to the external environment cannot be evaluated only by temperature, that is to say, the suitable temperature that people feel is not just a function of temperature. In order to fully express the influence of meteorology and environment on human body, it is necessary to use the human body heat balance model, in which all relevant meteorological elements, behavior parameters (activities and clothing) and human body parameters are fully considered, which breeds human body comfort. Human comfort is calculated by the influence of meteorological factors such as temperature, relative humidity and wind speed.

So how high can people tolerate?

The limit temperature of body temperature regulation at rest is 3 1℃ (85% relative humidity), 38℃ (50% relative humidity) and 40℃ (30% relative humidity). That is to say, if the limit temperature is exceeded, the body function will be damaged and symptoms-heatstroke or some complications will appear. But different people have different high temperature resistance limits. The above is the limit temperature of the general population, but for children, the elderly, the disabled and patients with chronic diseases, their heat resistance limit will be reduced because of their imperfect thermoregulation function, or their function decline or dysfunction. Therefore, in hot weather, these people should pay special attention to heatstroke prevention and cooling.

The influence of high temperature weather on human health is mainly heatstroke and death caused by cardiovascular and cerebrovascular diseases. Under the action of excessive ambient temperature, the thermoregulation mechanism temporarily fails, leading to heat accumulation in the body and heatstroke. According to the symptoms and degree of heatstroke, it can be divided into: heatstroke is the mildest manifestation of heatstroke and the most common; Thermal radiation refers to long-term work in a high temperature environment, which leads to vasodilation and congestion of the lower limbs, leading to fainting; Heatstroke is caused by long-term exposure, which leads to perspiration dysfunction.

For patients with hypertension, cardiovascular and cerebrovascular diseases, in the environment of high temperature, humidity, no wind and low pressure, perspiration is inhibited, the stored heat in the body is increasing, and the myocardial oxygen consumption is increasing, which makes the cardiovascular system in a state of tension. The sweltering heat can also lead to vasodilation and increased blood viscosity, which is prone to symptoms such as cerebral hemorrhage, cerebral infarction and myocardial infarction, and may lead to death in severe cases. According to the investigation of cardiovascular and cerebrovascular diseases in Beijing, it is found that hot and humid weather is a dangerous weather that leads to ischemic stroke.

It's sultry in summer, and it's also prone to colds (Xia Han), diarrhea, skin allergies and other diseases. The reason is that in the high temperature environment, human metabolism is vigorous, energy consumption is large, and sultry heat often makes people lack sleep and lose appetite, which leads to the decline of human immunity. At this time, if you don't control the use of air conditioners or electric fans to relieve summer heat, the human body will be in a low temperature environment for a long time, and its adaptability and resistance will decrease, and germs and viruses will take advantage of it and easily cause upper respiratory tract infections (colds). In addition, in the high temperature and high humidity environment, bacteria, viruses and other microorganisms multiply in large quantities, and food is easy to deteriorate, which will cause indigestion, acute gastroenteritis, dysentery, diarrhea and other diseases after eating; When people come home from the outdoor high temperature environment, they are used to turning on the air conditioner or directly blowing it with an electric fan and eating some iced food. This cold and heat will take effect immediately, and diarrhea will begin immediately. The sultry weather makes people sweat poorly, and it is also easy to cause skin allergies, especially for children below 10, mainly papular urticaria, eczema, contact dermatitis and so on. These are all caused by children's poor adaptability to high temperature and high humidity weather, as well as mosquito bites, pollen and dust allergies. In addition, indigestion, indigestion and parasites can also cause diseases. [4]

preventive measure

35 degrees Celsius is a threshold in hot weather. In daily life, whether cold or hot will cause discomfort to the body. People's normal body temperature is maintained at around 36-37℃. According to experiments in various countries, the comfortable temperature of human body is 19℃~24℃ in summer and 12℃~22℃ in winter. Therefore, in the hot summer, when the humidity is high and the temperature reaches 35℃, people need to pay attention. When the temperature and humidity reach a certain limit, the human body's heat cannot be dissipated, and the body temperature will rise, exceeding the human body's tolerance limit, causing fatal accidents.

In hot weather, people will experience a lot of sweating, which is very easy to get heatstroke or collapse. Old, weak, sick and young people should reduce outdoor activities and pay attention to drink plenty of water to replenish body moisture. When the weather is hot, a lot of sodium and potassium in the human body are lost with the discharge of sweat, which can cause electrolyte imbalance; The loss of vitamin C, vitamin B 1 and vitamin B2 in human body with sweat can cause nutritional metabolism disorder. The increase of protein decomposition in human body will cause the increase of energy consumption. Therefore, it is very important to ensure the nutritional needs and reasonable diet of human body in high temperature weather for maintaining the physiological function, metabolic activity and electrolyte balance of the body, adapting to the high temperature working environment and living environment, and ensuring health. First of all, replenish water. When the temperature is 36℃ ~ 38℃ in summer, people engaged in outdoor manual labor should replenish water 10L ~ 12L every day. People who are engaged in indoor work should supplement 2L~3L ~ 3 L of water every day. Drinking less water should not be more, so as not to affect appetite. In addition, a lot of sweating will also lead to the loss of inorganic salts, so inorganic salts should be supplemented while hydrating. At the same time, we should pay attention to increasing the intake of vitamin C, protein and energy. [5]

A reasonable diet can make you healthy. People use electric fans and air conditioners as tools to cool off the heat, so what can they drink to cool off the heat? Here are some simple and easy methods to recommend. Drinking tea is the best way to cool off the heat. Whether it is black tea, green tea or chrysanthemum tea, if it is accompanied by rock sugar, hawthorn, orange peel, cassia seed and so on. It is not only delicious, but also a good way to clear away heat and relieve summer heat. In summer, people don't like greasy food and tend to be light, so all kinds of porridge products have become the public's favorite. It is a good choice to prepare several nutritious and delicious porridge products for heatstroke prevention and cooling. For example: millet mung bean porridge, bitter melon porridge, corn porridge, mint porridge, lotus seed porridge, lily porridge and so on. At the same time, it is also a good choice to drink mung bean soup, lily soup, sour plum soup and bitter melon soup in summer. In addition, drinking fruit juice often in hot weather also has a good effect on promoting fluid production and quenching thirst, clearing away heat and detoxifying, which can be described as killing two birds with one stone. Common peach juice, pear juice, apple juice, grape juice, strawberry juice, watermelon juice and other juices can be drunk in moderation.