Why does Chengdu have so few sunny days? Is there any climate or geographical reason?

Because Chengdu is a basin, the salient features of the climate in the Sichuan Basin are:

Compared with areas at the same latitude, the annual average temperature is significantly higher, especially in winter, due to the cold air. Blocked by the Daba Mountains in the Qinling Mountains in the north, the average winter temperature in the Sichuan Basin is much higher than that in the middle and lower reaches of the Yangtze River, and is equivalent to that in northern Guangdong. The annual accumulated temperature is higher than that at the same latitude, and the frost-free period is also longer than that at the same latitude.

In a closed basin, the surrounding mountainous area in the southeast is relatively low, which is conducive to the entry of water vapor, while the mountainous area in the northwest is relatively high, which is not conducive to the dissipation of water vapor, resulting in high air humidity, rainy weather, and fog, which is the most sunny place in my country every year. One of the areas with the least hours (the other area with the least sunshine is Guizhou).

The closed terrain results in low wind speeds all year round in the Sichuan Basin, which is one of the regions with the smallest annual average wind speed in my country.

The climate in the eastern and western Sichuan Basin has many similarities but also differences. The east is generally rainy from May to June (similar to the plum rain in the south of the Yangtze River). From July to August, it is controlled by the subtropical high pressure, causing high temperatures and droughts, making it one of the regions with the highest summer temperatures in China. The west is prone to spring droughts from April to May, with temperatures from July to August It is rainy every month due to the influence of southwest warm and humid air flow.