1. Snow and Dayan River are similar in image characteristics.
Dayanhe is a simple, hardworking and unknown rural woman. Her image is similar to Xue. Snow is a pure, quiet and quiet natural element, which is similar to the image characteristics of Dayan River, so Ai Qing will think of Dayan River when he sees snow.
2. Snow is related to the living environment of Dayan River.
Dayanhe lives in the northern countryside of China, where it often snows in winter. Therefore, snow is closely related to the living environment of Dayan River. Ai Qing recalled the Wild Goose River, and naturally thought of the snow scene, which triggered his nostalgia for the Wild Goose River.
Snow is symbolic.
In literary works, snow is often endowed with some symbolic meanings, such as purity, beauty and tranquility. Ai Qing mentioned "snow" in his poems, or he may be using the symbolic meaning of snow to express his good memories and deep nostalgia for Dayan River.
To sum up, Ai Qing said in "Wild Goose River-My Nanny" that "I think of you when I see snow", instead of seeing spring rain or hearing the bleak voice of autumn wind, because the image characteristics of snow and Wild Goose River are similar, which is related to the living environment of Wild Goose River, and snow is symbolic.