Why does it often rain in Sichuan 365 days a year?

"Sichuan is a basin topography. At night, the air around the mountainside drops rapidly. Due to the high density of cold air, it sinks to the bottom of the basin, causing the warm and humid air at the bottom to rise and form convective rain. Note: Convective rain is a precipitation phenomenon caused by atmospheric convection, also known as thermal thunderstorm. Its formation mechanism is that the air in the near-surface layer is heated or the air in the upper layer is strongly cooled, which causes the air in the lower layer to rise and the water vapor to cool and condense, thus forming convective rain.