Cold dew is the seventeenth solar term among the twenty-four solar terms in the lunar calendar, and is the fifth solar term in autumn.

Hanlu is a solar term that reflects the characteristics of climate change. Han refers to cold. It can be seen from the literal meaning that the weather at this time has obviously become colder. Compared with the white dew period, the temperature has dropped a lot, and the dew on the ground is also colder. It is likely to become freezing dew, so it is called cold dew. Generally, the cold dew season falls on October 8 or 9 of the Gregorian calendar every year. On the day of the cold dew, the sun reaches 195 degrees of ecliptic longitude.

The three solar terms of white dew, cold dew and frost all represent the phenomenon of water vapor condensation. During this season, temperatures continue to drop in most parts of southern China. The average daily temperature in South China is less than 20°C. Even in areas along the Yangtze River, the temperature is difficult to rise above 30°C, while the lowest temperature can drop below 10°C. Except for a few river valleys and lowlands, the average temperature in the northwest plateau is generally below 10°C. According to the climatological standard for dividing the four seasons, it is already winter.

The impact of the cold dew solar term on the climate

After the cold dew, the cold air in the north has a certain influence. Most areas of our country are under the control of cold high pressure, and the rainy season has ended. The weather is often warm during the day, cool at night, and has clear skies, which is very beneficial to the autumn harvest. Thunderstorms have disappeared in most areas of mainland my country, and thunder can still be heard in some parts of Yunnan, Sichuan and Guizhou. The precipitation in October in North China is generally only half or less than that in September, while in northwest China it is only a few millimeters to more than 20 millimeters.

Hainan and southwest regions generally still experience continuous autumn rain at this time. In a few years, rainy weather also occurs in Jianghuai and Jiangnan, which has a certain impact on autumn harvest and autumn planting. Harvest cotton as soon as the weather is fine. In years when the temperature drops early, cotton can be collected when the temperature is not too low. The single-crop late rice in Jianghuai and Jiangnan is about to mature, and the double-crop late rice is filling. Pay attention to intermittent irrigation to keep the fields moist.