According to scientific standards, the continuous high temperature of 35℃ and above is called "heat wave", which belongs to meteorological disasters. The ancients called it a "heat disaster", but the eight years of Qianlong, which is called "the hottest summer in China", is extremely rare in the whole history of China. In the afternoon of July 20th to 25th, the temperature 1743 was above 40℃. Among them, the temperature on July 25th was the highest, reaching an astonishing 44.4℃.
According to the Records of Fushan County, "It is hot in summer and May, and many pedestrians die, especially in the capital, and some vendors drifting in Beijing are also hot." At that time, Qianlong took advantage of the trend and wrote the first famous sentence: "Ice tray snow pole, turn cold light." The exhibition is bitter and annoying, and my heart is next to Li Xi. " In this poem, Gan Long fully expressed his sympathy for the people to appease them.
Causes and effects of heat wave
The weather system has started. Due to the prevailing downdraft of subtropical high, the temperature rises strongly, the pressure gradient is small, and there is almost no wind. In areas controlled by subtropical high, cloudy and hot weather is often dominant. Urban heat island effect, due to the dense population and large building area, makes the humidity and air convection on the urban surface change, resulting in the temperature of the city being significantly higher than the surrounding area, which plays a role in fueling the high temperature weather.
High temperature and summer heat force early rice to mature at milk maturity stage, reduce 1000-grain weight and yield; Due to the increase of transpiration, the imbalance of water supply and demand, cotton wilting, bud dropping and boll dropping, and high temperature injury are unfavorable to the growth of vegetables and other crops. The high temperature and summer heat greatly increased the water and electricity consumption of urban residents. For example, the daily water supply in Shanghai 1988 during the high temperature period exceeded the highest level in history, of which the sunrise water in July 18 was 4.65 million tons, and many water supply equipment failed due to overload operation.