Sichuan is located in the transitional zone between China’s Qinghai-Tibet Plateau and the eastern plains and therefore has complex and varied topography. The vertical altitude difference between the highest point and lowest point reaches up to over 7,000m. And Sichuan’s complex and diverse climates result in rather obvious regional difference and vertical change in landscape and there are distinct disparities between the east and the west. Sichuan is generally divided into three major climate zones:
1. Humid Subtropical Climate Zone of Sichuan Basin
It is humid and warm throughout the year. The annual average temperature is 16-18℃ and the accumulated temperature is 4000-6000℃, with narrow daily range of temperature and wide annual range of temperature. It is warm in winter and hot in summer and the frost-free period here lasts for 230 to 340 days. Moreover, there are many cloudy days and few sunny days, and therefore the sunshine duration is short with the annual sunshine duration of merely 1000 to 1400 hours, which is 600 to 800 hours less than that of the areas along the lower reaches of the Yangzte River at the same latitude. There is abundant rainfall here, with the annual rainfall of 1000 to 1200 mm. Half of the rainfall happens in summer and more often than not at night.
2. Sub-Humid and Subtropical Climate Zone of Southwest Sichuan’s Mountainous Regions
The temperature is high throughout the year and the annual average temperature is 12-20℃,with wide daily range of temperature and narrow annual range of temperature. It is cold in the morning and warm at noon and the four seasons here are not clearly defined. Beside, there are few cloudy days and many sunny days and therefore the sunshine duration is long with the annual sunshine duration of 2000-2600 hours. With a little rainfall, the wet and dry seasons are distinct here and 7 months of a year are dry seasons with the annual rainfall of only 900 to 1200 mm. 90% of the rainfall happens from May to October. Influenced by the foehn, the valley regions have a typical dry-hot valley climate and a notable three-dimensional climate is formed in the mountainous regions.
3. Alpine Climate Zone of High Mountains and Plateaus of Northwest Sichuan
This region has huge altitude difference and obvious three-dimensional changes in climate. Subtropical climate, warm-temperate climate, moderate-temperate climate, cold-temperate climate, subfrigid climate, frigid climate and permafrost climate take turns to appear from the valley to the mountain ridge. On the whole, the cold temperature climate is dominant, which is characterized by warm and dry valleys, cold and wet mountains, chilly winters and cool summers as well as insufficient rainfall and heat. The annual average temperature is 4-12℃ while the annual rainfall is 500-900 mm. It is often fine with sufficient sunlight and the annual sunshine duration reaches 1600-2600 hours.
The overall characteristics of Sichuan’s climate can be summarized as follows: monsoon climate is obvious and rain and heat happens in the same seasons; regional climate difference is prominent in that the east is characterized by warm winters, early springs, hot summers, autumn rains, much cloud and fog, little sunshine and a long growing season and the west is characterized by coldness, long winters, almost no summer, sufficient sunshine, concentrated rainfall and distinct dry and rain seasons; vertical climate changes are significant and climate types are varied, which are good for the comprehensive development of agriculture, forestry and husbandry; and meteorological disasters happen in various forms with a high frequency and large scope, which are mainly droughts, rainstorms, floods and cold weather. (The above data are provided by the Sichuan Yearbook Press. See Sichuan Yearbook 2008 for more details.)