Is the Sichuan Basin really a maritime climate?

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, Hubei and Guizhou at the same latitude. Extreme minimum temperature -6 ~-2℃. Frost and snow are scarce, and the frost-free period is 280 ~ 350 days throughout the year. In winter, there is constant frost and snow in Wuhan at the same latitude, and Changning, whose basin is located in the Yangtze River basin, is frost-free all the year round. Summer in all parts of the river basin begins at the end of May and lasts for more than 4 to 5 months. The temperature is high in the east and low in the west. The summer temperature in the west is 3-4 degrees lower than that in Shanghai, Wuhan and other cities at the same latitude, but the humidity is unbearable. The average temperature is around 25℃, with high temperature in the southeast and low basin edge. The temperature is as high as 26 ~ 29℃ in the hottest month, and nearly 30℃ 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℃, which is equivalent to the tropical climate of 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.