What does it mean to seal the land with light snow and seal the river with heavy snow?

"Small snow closes the land and heavy snow closes the river" means that although there will be snowfall and the temperature will drop after the light snow solar term, the snowfall and cooling rate will not be obvious. After the snowfall, there will be some residual snow on the ground and the land will be slightly frozen.

The closure of the river by heavy snow means that not only the snowfall will increase, but also the temperature will drop significantly after the heavy snow solar term, and the water in the river will slowly freeze. After it snows, you can see snow not only on the ground, but also on the river.

relevant information

After the solar term of heavy snow, with the increase of snowfall, the temperature began to drop significantly. After the solar term of heavy snow, the temperature in many northern areas will drop to about-10 degrees at night, and the temperature will hover around three or four degrees above zero during the day. As the ground temperature drops, the river will start to freeze as the temperature drops below zero.

Because the snowfall weather will increase and the snowfall will increase after the heavy snow festival, snow can be seen not only on the ground but also on the frozen river surface after the heavy snow festival.