Why are foggy and cloudy days common in the Sichuan Basin?

The Sichuan Basin is characterized by frequent fog and many cloudy days primarily due to its unique topography and atmospheric conditions. The region is surrounded by high mountains—including the Plateau of Tibet to the west and the Daba Mountains to the north—which shelter the basin from cold polar air masses and northern winds.12

This protective enclosure results in a relative absence of wind and high levels of relative humidity. These factors, combined with the basin's geography, contribute to the persistent overcast conditions that are so common in the region that there is a local saying: "Sichuan dogs bark when they see the Sun."1