Is it related to the water after the snow melts? Or is it related to the cooling after the snow melts? Which plays a decisive role?

It is related to the water after snow melting or the temperature drop after snow melting, but the water after snow melting plays a decisive role.

It's cold in winter, and the snow often doesn't melt easily. The snow covered on the soil is soft, and there is a lot of stagnant air hidden inside. Air doesn't transfer heat, just like covering a quilt for crops. No matter how cold it is outside, the temperature below will not drop very low. Covered with winter snow, it is not easy to attract pests.

After the cold wave, the weather gradually warmed up and the snow gradually melted. This not only protects crops from freezing damage, but also keeps the water melted by snow in the soil, saving a lot of water for crops, which is very beneficial to spring ploughing and sowing and the growth and development of crops.