Why is Sichuan so humid?

Sichuan basin is located in the subtropical monsoon climate zone, and the climate should be warm and humid. In addition, the special topography of the basin: the southeast of the closed basin is relatively low, which is conducive to the entry of water vapor, while the northwest mountain is relatively high, which is not conducive to the loss of water vapor, resulting in high air humidity; As well as the closed terrain, the wind speed in Sichuan Basin is low all the year round, which is one of the areas with the lowest annual average wind speed in China. Therefore, the Sichuan Basin is prone to foggy weather due to its high water vapor and low wind.

The terrain of Sichuan basin is closed, and the temperature is higher than other areas at the same latitude. The average temperature in Leng Yue is 5 ~ 8℃, which is 2 ~ 4℃ higher than that in Shanghai, Wuhan in the same latitude and Guiyang in the south latitude. Extreme minimum temperature -6 ~-2℃. Frost and snow are scarce, and the frost-free period is 280 ~ 350 days throughout the year. Changning, located in the Yangtze River valley, is frost-free all year round. Summer begins at the end of May and lasts for more than 4 ~ 5 months. The temperature in the hottest month is as high as 26 ~ 29℃, the Yangtze River basin is nearly 30℃, and the extreme maximum temperature in the southeast of the basin often exceeds 40℃. Chongqing and Pengshui used to have 44℃, so Chongqing is also one of the three "stoves" in the Yangtze River Basin. The sunny, hot and high temperature weather in midsummer caused a severe summer drought in the southeast of the basin. The annual average temperature is 16 ~ 18℃. The active accumulated temperature above 10℃ is 4500 ~ 6000℃ and lasts for 8 ~ 9 months, belonging to the middle subtropical zone. The accumulated temperature in the southeast Yangtze River basin exceeds 6000℃, for example, the accumulated temperature in Qijiang River exceeds 6 100℃, which is equivalent to the tropical climate in South Asia south of Nanling in China. The temperature in the basin is high in the east and low in the west, high in the south and low in the north, high in the bottom and low in the edge, and the isotherm distribution is concentric. The temperature in the mountainous area on the edge of the basin has vertical distribution characteristics. The elevation of Emei Mountain and Jinfo Mountain rises by 100 m, and the temperature drops by 0.55℃ and 0.6 1℃ respectively. The average annual temperature at the top of Mount Emei is only 3℃, and the active accumulated temperature above 10℃ is 586℃, which is equivalent to cold temperate zone and sub-cold zone in climate. The annual precipitation in Sichuan Basin is 65,438+0,000 ~ 65,438+0,300 mm, and the precipitation in the mountainous areas around the basin is very rich. For example, the annual precipitation in the western mountainous area between Leshan and Ya 'an is 1.500 ~ 1.800mm, which is a prominent rainy area in China and is called "West China Rain Curtain". However, winter drought, spring drought, summer waterlogging and autumn Mao Mao rain are unevenly distributed in the year, and 70 ~ 75% of the rainfall is concentrated in 6 ~ 10. The maximum daily precipitation can reach 300 ~ 500mm. "Night rain" has been famous since ancient times, and it accounts for more than 60 ~ 70% of the total rainfall. The fog in the basin is big and wet, and the clouds are low and cloudy. Emei Mountain and Jinfo Mountain are the foggy areas in China, and the annual relative humidity is also the highest in China. The annual sunshine in the basin is only 900 ~ 1300 hours, and the annual solar radiation is 370 ~ 420 KJ/cm2, both of which are the lowest in China, so it is called "the tree spring barks at the sun".