Why is Chongqing called the furnace city?

Geographical reasons. In summer, the Yangtze River valley in China is hot and dry, and the sun is like fire. The coastal cities of Nanjing, Wuhan and Chongqing are vividly called "three furnaces". The relevant departments call the days when the highest temperature is higher than 32℃ as "hot summer days" and the days when the highest temperature is higher than 37℃ as "extremely hot days". The extreme maximum temperatures in Nanjing, Wuhan and Chongqing are all above 40℃, including 4 1.3℃ in Wuhan, 43℃ in Nanjing and 44℃ in Chongqing. Why is it so hot? Some meteorologists believe that there are three reasons for the formation of the "three furnaces": First, during the whole summer drought period, the plum rains in the middle and lower reaches of the Yangtze River have passed, and the upper air is controlled by the subtropical high. When the upper air current sinks, the temperature rises gradually, the advection is weak, and the wind force is extremely small. In addition, the sky is cloudless in Wan Li, blue and Wan Li, and the vicious sun is scorching the earth. The earth also conducts high temperature into the air, which makes the temperature rise, which is the main reason for the formation of "stoves". Second, these three cities are all in the Yangtze River basin, and their positions are very low, as if at the bottom of the pot. The air density here is very high. The dense atmosphere does not weaken the solar radiation incident during the day, but it prevents a lot of ground heat from radiating and cooling into the air at night, making it difficult for the ground to dissipate heat, which is another reason for the formation of a "stove". Third, these three cities are located along the Yangtze River, surrounded by rice fields and ditches. Under the strong sunlight, water evaporates quickly, which increases the air humidity. With regard to the human body's feeling of temperature and humidity, some people have done experiments: when the air relative humidity is lower than 60% and the temperature is higher than 35℃, people will feel hot, but when the relative humidity is 70%-80% and the temperature is 3 1℃, people will start to feel hot. When the relative humidity exceeds 80%, the temperature of 29℃ is the index temperature of mugginess.