Many readers have the experience that precipitation is unevenly distributed in a day, and it is particularly easy to rain in some periods, while it is very little in some periods, which is the daily variation of precipitation.
The earliest mentioned phenomenon of daily variation of precipitation is "late rain", which is reflected in the poems of Tang Dynasty. Perhaps the most famous is the romantic artistic conception of "when you cut candles at the west window, but talk about the rain at night" described in Li Shangyin's Notes to Friends in the North on a Rainy Night. Bai Juyi's "Song of Eternal Sorrow" also has such a narrative: "Only the water in Shu is evergreen, the mountains are evergreen, and your love remains unchanged, deeper than the sky; He stared at the desolate moon from his temporary palace, and he heard the bells in the late rain cutting his chest. "
In addition, Li Bai, Wang Wei and other poets in the past dynasties also mentioned the characteristics of night rain in Sichuan. Combined with modern observation data, it is also confirmed that the phenomenon of night rain exists in Sichuan basin and even in many areas in southwest China, indicating that the phenomenon of night rain in Sichuan has existed since ancient times and is not a phenomenon only today.