[High temperature science five] What is a high temperature heat wave？
In meteorology, the daily maximum temperature reaches or exceeds 35℃ as the standard of high temperature, and "high temperature heat wave" is also called high temperature heat wave, which is a meteorological term. It usually refers to the high temperature weather above 35℃ that lasts for many days. Because of the long duration of high temperature, people, animals and plants cannot adapt and have adverse effects. The standard of high temperature heat wave is mainly based on the degree of influence or harm caused by high temperature to human body.
High temperature is also a common meteorological disaster. In addition to the Qinghai-Tibet Plateau and other parts of China, high temperature weather has occurred in almost all places, including the northernmost Mohe (high temperature weather occurred five times in June 2010). The hot weather in China is mainly concentrated from May to October. Geographically, Jiangnan, South China, Southwest China and Xinjiang are all frequent places of high temperature. According to the statistics from 1951 to 2009, among the cities above the provincial level in China (except Lhasa, where there is no high temperature weather), Chongqing has the most frequent occurrence, reaching 1853 days; Xining is the least, only 3 days. Xinjiang basin in China is also a frequent place of high temperature, such as Turpan, where it is high temperature all day in the whole month (June, July and August) for many times.
In midsummer, the middle and lower reaches of the Yangtze River are under the control of the western Pacific subtropical high, and there is hot weather, which is the hardest hit by the summer heat wave in China. In July and August after the rainy season, there will be 20 to 30 days of high temperature weather in general years, and the number of high temperature days in short rainy years can exceed 40 days. In recent 50 years, the national average high temperature days showed a trend of decreasing first and then increasing. From 1950s to early 1980s, the number of high temperature days decreased, and it began to show an obvious increasing trend in the early 1980s. There is a linear increase trend in the number of high temperature days in northwest and north China, especially in South China.
High temperature has a certain impact on people’s daily life and health and all sectors of the national economy. High temperature and heat wave make people feel uncomfortable, work efficiency is low, and the incidence of heatstroke, intestinal diseases and 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 intensifies soil water evaporation and crop transpiration. When high temperature and little rain occur at the same time, it causes serious soil moisture loss, accelerates the development of drought and has a great impact on agricultural production. Continuous high temperature and lack of rain are also easy to cause fires, and forest fires will damage the ecological environment. In addition, tourism, transportation, construction and other industries will also be affected to varying degrees, but the high temperature and heat wave will also bring business opportunities to some manufacturers and businesses that produce and sell heatstroke prevention and cooling supplies and equipment.
High temperature heat wave standard
The standard of high temperature heat wave is mainly based on the degree of influence or harm caused by high temperature to human body.
The disaster of high temperature and heat wave is influenced by geography, society and economy. Different countries and regions in the world adopt 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.
Standard of high temperature heat wave in China
In China, it is generally called high temperature when the daily maximum temperature reaches or exceeds 35℃, and the high temperature weather process for several days (more than 3 days) is called high temperature heat wave (or called high temperature heat wave). Due to the frequent occurrence of high temperature and heat wave weather 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 for the defense of 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 standards for high temperature heat waves
WMO (World Meteorological Organization) suggested that the standard of high-temperature heat wave is: the maximum daily temperature is higher than 32℃ and lasts for more than 3 days.
The Royal Dutch Institute of Meteorology has determined that 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 warnings based on 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 three hours for two consecutive days or the predicted thermal index exceeds 46.5℃ at any time.
Based on the human heat balance model, German scientists have formulated the human body temperature index. For example, when the physiological equivalent temperature (PET) of human body exceeds 41℃, the thermal mortality rate increases significantly. Therefore, the physiological equivalent temperature (PET) of human body is greater than 41℃ as the early warning standard of high temperature heat wave.
High temperature heat wave type
Because the human body’s feeling of hot and cold depends not only on the 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 heat type and muggy type.
Dry-hot high temperature
High temperature weather with extremely high temperature, strong solar radiation and low air humidity is called dry-hot high temperature. In summer, northern China such as Xinjiang, Gansu, Ningxia, Inner Mongolia, Beijing, Tianjin, Shijiazhuang and other places often appear.
Muggy 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 high temperature. Because people feel like taking a sauna in a sauna in this weather, it is also called "sauna day". It often appears in China’s coastal areas, the middle and lower reaches of the Yangtze River, and southern China.
High temperature hazard
High temperature and heat wave make human body unable to adapt to the environment and exceed the tolerance limit of human body, which leads to the occurrence or aggravation of diseases and even death, and animals are the same; At the same time, high temperature and heat wave can also affect the growth and development of plants and reduce crop production. The high temperature heat wave process will also aggravate the occurrence and development of drought; The amount of water and electricity used has increased sharply, which has a great impact on people’s life and production. In addition, high-temperature heat waves often make people feel irritable, and even appear delirious, which is easy to cause public disorder, accidents, casualties, poisoning, fires and other incidents, which are indirect effects of high-temperature heat waves.
The influence of meteorological conditions on human body in the environment is the result of the comprehensive action of many meteorological factors. For example, people’s comfort to the external environment can’t be evaluated only by the temperature, which means that the appropriate temperature that people feel is not only the function of the temperature. In order to fully express the influence of meteorology and environment on human body, we must 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 through the influence of meteorological factors such as temperature, relative humidity and wind speed.
So how high can people tolerate? The limit temperature of human body temperature regulation at rest is 31℃ (85% relative humidity), 38℃ (50% relative humidity) and 40℃ (30% relative humidity), that is to say, beyond the limit temperature, human body function will be damaged, and symptoms-heatstroke or some complications will appear. But the limit of high temperature resistance of different people is different. What is given above is the limit temperature of the general population, but for children, the elderly and the infirm, and patients with chronic diseases, their heat resistance limit will be reduced due to their imperfect body temperature regulation function, or their functional decline or dysfunction. Therefore, in hot weather, these people should pay special attention to heatstroke prevention and cooling.
The main effects of high temperature weather on human health are heatstroke and death caused by cardiovascular and cerebrovascular diseases. Under the action of too high ambient temperature, the body temperature regulation mechanism temporarily breaks down, resulting in heat accumulation in the body, leading to heatstroke. According to the symptoms and degree of heatstroke, it can be divided into: heat collapse, which is the mildest manifestation of heatstroke and the most common; Thermal radiation refers to long-term work in high-temperature environment, which leads to vasodilation and blood stasis of lower limbs, resulting in fainting; Sunstroke is caused by long-term exposure, which leads to perspiration dysfunction.
For patients with hypertension, cardiovascular and cerebrovascular diseases, in a high temperature, humid, windless and low pressure environment, human perspiration is inhibited, the heat stored in the body is increasing, and the oxygen consumption of the myocardium is increasing, which makes the cardiovascular system in a state of tension. The sultry heat can also lead to vasodilation and increased blood viscosity, which is prone to cerebral hemorrhage, cerebral infarction, myocardial infarction and other symptoms, and may seriously lead to death. 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.
In the sultry weather in summer, it is also prone to diseases such as cold (summer cold), diarrhea and skin allergy. The reason is that under the high temperature environment, human metabolism is vigorous, energy consumption is high, and sultry heat often makes people lack sleep and lose appetite, which leads to the decline of human immunity. At this time, if air conditioners or electric fans are not used sparingly 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 infection (cold). In addition, in high temperature and high humidity environment, bacteria, viruses and other microorganisms breed in large quantities, and food is easily spoiled, which will cause diseases such as indigestion, acute gastroenteritis, dysentery and diarrhea after eating; When people return home from the outdoor high temperature environment, they are used to turning on the air conditioner or blowing it directly 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 under 10 years old, mainly papular urticaria, eczema, contact dermatitis, etc., which are 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.
preventive measure
The high temperature of 34℃ is a threshold. In daily life, both cold and heat will cause physical discomfort. People’s normal body temperature is maintained at about 37℃. According to experiments in various countries, the comfortable temperature for human body is 19℃~24℃ in summer and 12℃~22℃ in winter. Therefore, in hot summer, when the humidity is high, people need to pay attention when the temperature reaches 34℃. When the temperature and humidity reach a certain limit, the human body’s heat can’t be dissipated, and the body temperature will rise, which will exceed the human tolerance limit and cause fatal accidents.
In hot weather, people will experience a lot of sweating, which is very prone to heatstroke or collapse. Old, weak, sick and young people should reduce outdoor activities and pay attention to drinking more water to replenish body water. In hot weather, a large amount of sodium and potassium in the human body are lost with the discharge of sweat, which can cause electrolyte imbalance; Vitamin C, vitamin B1 and vitamin B2 in human body are lost with sweat, which can cause metabolic disorder of nutrients. The increase of protein decomposition in human body can cause the increase of energy consumption. Therefore, it is very important to ensure that the human body’s nutritional needs and diet are reasonable in high temperature weather, so as to maintain the body’s physiological function, metabolic activity and electrolyte balance, adapt to the high temperature working environment and living environment, and ensure health. First of all, we must replenish water. In summer, when the temperature is 36℃ ~ 38℃, people who are engaged in outdoor manual labor should replenish 10L ~ 12L of water every day. People who are engaged in indoor work should replenish 2L～3L ~ 3 L of water every day. The appropriate amount of water should be less and more times, so as not to affect appetite. In addition, a lot of sweating will also cause the loss of inorganic salts, so inorganic salts should be supplemented while supplementing water. At the same time, it should be noted that the intake of vitamin C, protein and energy should be increased.
A reasonable diet can make you healthy. People use electric fans and air conditioners as tools to cool off the heat, so what can "drink" to relieve the heat? Here are some simple and easy methods to recommend. Drinking tea is the best way to relieve summer heat. Whether it is black tea, green tea or chrysanthemum tea, if it is accompanied by rock sugar, hawthorn, orange peel, cassia seed, etc., it not only tastes excellent, but also is a good way to clear away heat and dispel summer heat. In summer, people don’t like greasy food and tend to be light, so all kinds of porridge products have become the favorite food of the public, so 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, etc. At the same time, drinking more foods such as mung bean soup, lily soup, sour plum soup and bitter melon soup in summer is also a good choice to cool down; In addition, drinking fruit juice often in high temperature weather also has a good effect on promoting fluid production to quench 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.
High temperature economy
High-temperature economy refers to the phenomenon that "cool consumption" for heatstroke prevention and cooling has been popular all the way in the city due to the long-lasting high-temperature weather, the sales of household appliances have increased greatly, sunscreen products have been popular, the swimming pool business has been booming, and taxi drivers have ushered in a new round of business season.
Appliance industry
The sales of household appliances have greatly increased. Under the scorching sun, it seems that no one will care about their wallets and find that air conditioners and electric fans are extremely hot. People who come to consult and buy air conditioners and fans are in an endless stream. In order to attract consumers’ attention and meet the needs of energy saving and emission reduction, many businesses on air-conditioning shelves have launched energy-saving air-conditioning series.
cosmetic industry
Sunscreen products are popular, and the continuous high temperature in summer also drives the sales of all kinds of sunscreen products to rise. In some big shopping malls and supermarkets, sunscreen and other sunscreen products have become popular necessities for the public. The hot summer is a very nerve-racking season for women who love beauty. In summer, ultraviolet rays are strong, and the skin is easy to be blackened and sunburned. In order to resist the attack of ultraviolet rays, sunglasses and sunscreen products have become essential items for women to go out. Many products are labeled as hot sale and promotion, and various skin care products such as moisturizing, whitening and sun protection occupy several counters. There are more and more kinds of sunscreen products, and all kinds of sunscreen cream and sunscreen spray are dazzling.
service industry
1. Taxis and swimming pools are booming. Due to the high temperature, many people who are used to walking choose to take taxis. The hot weather has ushered in a new round of business season for taxi drivers.
2. The business of restaurants and teahouses is booming. The temperature is high, so I can’t stand the heat of buying food and cooking, so I eat out. Food streets, restaurants, and night beer businesses are booming everywhere, and at night, people who eat in open-air places are in an endless stream. Compared with the warming of restaurant sales, the business of tea building is more prominent. In some hotels and teahouses, guests are often full from 1 pm to 10 pm.
3. Summer products such as watermelon, fruit, milk tea and cold drinks are favored by the residents. The hot weather often makes the sales of these cold and summer foods violent, and the sales volume has soared.
(Source: Weather Network Editor: Li Wenqin)