Climate conditions and causes in the Sichuan Basin
The Sichuan Basin has an occluded terrain. Because the Qinling Mountains in the north block cold air, the temperature in winter is higher than other areas at the same latitude. The average temperature in the coldest month is 3-5℃ in the north and 5-8℃ in the south, which is 1-4℃ higher than Shanghai, Hubei, Anhui and Guizhou at the same latitude. The extreme minimum temperature in the northern part of the basin is -8~-5℃, and the southern part is -5℃~-2℃. Frost and snow are rare, and the annual frost-free period is 280 to 350 days long. Wuhan at the same latitude has constant frost and snow in winter. Changning, whose basin is located in the Yangtze River Valley, is frost-free all year round. ?
Summer in various parts of the basin begins at the end of May and ends in mid-September. Summer lasts for four months, with temperatures higher in the east and lower in the west. The average summer temperature in the western part of the basin is about 25°C, which is 3-4°C lower than Shanghai, Wuhan and other cities at the same latitude, but the humidity is high, so the heat is unbearable. The temperature in the hottest month in the east is as high as 26~29℃, and in the Yangtze River Valley, it reaches 30℃ locally. Continuous sunny and high temperatures in midsummer caused severe summer drought in the southeastern part of the basin.
The temperature in the basin is higher in the southeast and lower in the northwest, and the basin bottom is higher and lower at the edge; the annual average temperature in various places is 16 to 18°C. The active accumulated temperature above 10℃ is 4500-6000℃ and lasts for 8-9 months. It belongs to the mid-subtropical zone. The accumulated temperature in the Yangtze River Valley in the southeast exceeds 6000°C, which is equivalent to the southern subtropical climate south of China's Nanling Mountains.
The temperature in the basin is high in the east and low in the west, high in the south and low in the north. The basin bottom is high and the edge is low. The isotherms are distributed in a concentric circle shape. The temperature in the mountains on the edge of the basin has vertical distribution characteristics. For example, as the altitude of Mount Emei and Jinfo Mountain increases by 100 meters, the temperature decreases by 0.55°C and 0.61°C. The annual average temperature on the top of Mount Emei is only 3°C, and the accumulated temperature for activities above 10°C is 586°C. The climate is equivalent to the cold temperate zone and subarctic zone.
Extended information:
The Sichuan Basin can be clearly divided into two parts: the marginal mountains and the basin bottom, with an area of approximately more than 100,000 square kilometers and more than 160,000 square kilometers respectively. There are many middle and low mountains in the marginal mountainous areas. The transitional elements of the landscape are obvious. For example, the composition of animals and plants includes elements from Central China, Southwest China, the Qinghai-Tibet Plateau, and North China. The edge mountain area generally has 2 to 5 vertical natural zones from bottom to top.
The edge mountains are the base for various economic trees and timber forests in Sichuan. Soil erosion is serious in agriculture. There are many hills, low mountains and plains at the bottom of the basin. The surface composition material is new and single, consisting of sandy mudstone and Quaternary sediments. The climate is mid-subtropical, and the heat is much higher than that of the edge mountains, but the precipitation is not as high as that of the edge mountains. The vegetation has been replaced by artificial secondary forests, the coverage rate is low, and the cultivated land is contiguous. Summer drought and floods are the biggest disasters in this area.
The internal topography of the basin shows obvious three-part characteristics, namely, the plain landform in the west of the basin, the hilly landform in the middle of the basin, and the mountainous landform in the east of the basin. The three are bounded by Longquan Mountain and Huaying Mountain.
Baidu Encyclopedia-Sichuan Basin