Chengdu is located on the vast land of the Chengdu Plain. And the Chengdu Plain is in the middle of the Sichuan Basin.
The Sichuan Basin is one of the four major basins in China. It is located in the central and southern parts of the Asian continent (between 28″10′ and 32.25′ north latitude), the middle abdomen of China and the middle eastern part of China’s Great Western.
The Sichuan Basin covers the central and eastern parts of Sichuan Province and most of Chongqing, also known as the Envelope Basin and the Purple Basin. The total area is about 260,000 square kilometers. It is surrounded by the Qinghai-Tibet Plateau, Daba Mountain, Wushan Mountain, Dagu Mountain and Yunnan-Guizhou Plateau. The mountainous area is between 1000m and 3,000m, with an area of about 100,000 square kilometers. The bottom of the basin is low, with an altitude of 250m to 750m and an area of about 160,000 square kilometers.Therefore, it can be clearly divided into two parts: the edge mountain and the bottom of the basin. The edge mountain area generally has 2 to 5 vertical natural zones from the bottom up. The northwestern edge is a long Longmen Mountains.
Chengdu Plain, also known as the Chuanxi Plain, the basin west plain, is called “Chuan xi ba zi”（meaning of West Sichuan Dam）in Sichuan dialect. It is an alluvial plain located in the western part of the Sichuan Basin in China, including all districts and counties in Chengdu, Sichuan Province, and Deyang and Mianyang. Some areas of Ya’an, Leshan, Meishan and other places, with a total area of 18,81 square kilometers, are the largest plains in the three provinces of southwest China.
The Chengdu Plain is developed on the northeast-southwestward syncline structure. The alluvial fan plains are composed of eight alluvial fans originating from the Minjiang River, the Lancang River and its tributaries in the northwestern Sichuan Plateau. The entire plain is loose, the sediment is thick, the terrain is flat, the average slope is only 3% to 10%, and the relative height difference of the surface is below 20 meters.
The Chengdu Plain is surrounded by mountains, the basement consists of the Cretaceous and Lower Tertiary clastic rocks (red layers), and the main material of the plain consists of Quaternary loose deposits. The four seasons are distinct in the plains, with less sunshine, mild climate and abundant rainfall. It belongs to the warm and humid subtropical Pacific southeast monsoon climate zone. Its water system has a special pattern and is spindle-shaped. After the river exits the mountain, it is divided into many tributaries to the plain, with branches intertwined and river channels.
The terrain of Chengdu Plain is inclined from the northwest to the southeast, generally about 600 meters above sea level, and the soil is fertile. There is also the Dujiangyan irrigation project, which is famous from ancient times. Chengdu Plain owns the developed agriculture, rich products are and the dense population. It is an important rice, sugar cane, silk and rapeseed producing area in China. It has been known as the “land of heaven” since ancient times.
Chengdu has a subtropical monsoon climate with the characteristics of early-coming spring, hot summer, cool autumn and warming winter. The annual average temperature is 16 °C and the annual rainfall is about 1000 mm. A notable feature of Chengdu’s climate is cloudy fog and short sunshine hours. Another remarkable feature of Chengdu’s climate is that the air is humid. Therefore, although the temperature is not high in summer (the highest temperature generally does not exceed 35 °C), it is sultry. In winter, the average temperature is above 5 °C, but because of the cloudy weather, the air is humid and very cold. The rainwater in Chengdu is concentrated in July and August, and it is dry and less rainy in winter and spring, with little snow and ice.
The extreme minimum temperature in Chengdu is -5.9 °C. In most of the districts and counties, this typical climate appears in December, and some areas appear in January. The most windy direction in Chengdu in all year round is calm wind. In June, July and August, it is the north wind, and the rest of the month is the northerly wind in the northeast.