Why is it so rainy in Sichuan?

Sichuan is located in the subtropical zone. Due to the influence of geographical latitude and landform, the zonality and vertical direction of climate change obviously, and there is a great difference between the east and the west. According to the differences of water, heat and light conditions, it can be roughly divided into three climate zones:

1. The subtropical humid climate zone of Sichuan Basin, that is, the Sichuan Basin and its surrounding mountainous areas. This area is warm and humid all the year round, with an annual average temperature of 16 ~ 18℃, a daily temperature of ≥ 10℃ lasting for 240 ~ 280 days, a cumulative temperature of 4,000 ~ 6,000℃, a small daily temperature difference, a large annual temperature difference, warm in winter and hot in summer, and a frost-free period of 230 ~ 340. There are many clouds in the basin, few sunny days, and the sunshine time in the whole year is short, only 1000 ~ 1400 hours, which is 600 ~ 800 hours less than that in the lower reaches of the Yangtze River basin at the same latitude. Abundant rainfall, annual precipitation 1000 ~ 1200mm.

The second is the subtropical semi-humid climate zone in the mountainous area of western Sichuan. The annual temperature in this area is relatively high, with an annual average temperature of 12 ~ 20℃. Annual range is small and the diurnal range is large. It is cold in the morning and warm in the afternoon. The four seasons are not obvious, and the dry and wet seasons are distinct. There is little precipitation, and there are seven dry months throughout the year. The annual precipitation is 900 ~ 1200mm, and 90% is concentrated in 5 ~ 10. There are few clouds, many sunny days and long sunshine hours, and the sunshine hours in the whole year are mostly 2000 ~ 2600 hours. Typical dry-hot valley climate is formed in the valley area affected by foehn, and obvious three-dimensional climate is formed in the mountain area.

Three, the alpine plateau alpine climate zone in northwest Sichuan. The altitude difference in this area is great, and the three-dimensional climate change is obvious. Subtropical zone, warm temperate zone, middle temperate zone, cold temperate zone, sub-cold zone and permafrost zone appear in turn from the valley to the ridge. Generally speaking, the climate is dominated by cold temperate zone, with dry and warm valleys, wet and cold mountains, cool Leng Xia in winter and insufficient water and heat. The annual average temperature is 4 ~ 12℃, the annual precipitation is 500 ~ 900 mm, the weather is clear and the annual sunshine 1600 ~ 2600 hours.

The general characteristics of Sichuan climate are: the monsoon climate is obvious, and the rain and heat are in the same season; The performance varies greatly from region to region. It is warm in winter in the east, hot in summer in early spring, rainy and cloudy in autumn, less sunshine, long growing season, cold in the west, long winter, basically no summer, abundant sunshine, concentrated precipitation and distinct wet and dry seasons. The vertical climate changes greatly and there are many climate types, which is conducive to the comprehensive development of agriculture, forestry and animal husbandry; There are many kinds of meteorological disasters with high frequency and wide range, mainly drought, and heavy rain, flood and low temperature often occur.