Why we need snow: The role of snowfall in pest control, soil protection
There is an old Chinese saying that the fall of seasonable snow promises a fruitful year. In early January this year, Beijing, Hebei and some other parts of northern China may not be able to wait for the first snowfall in 2023.
Snowfall is important for overwintering crops, and prolonged periods without snow can cause soil drought, adversely affecting the growth of winter wheat and other crops.
Snow is loose and porous, like a soft quilt that the soil and crops from exposure to the cold air. It also can prevent the loss of heat in the soil.
Winter snow also affects the survival of overwintering pests in the soil. After a heavy snowfall covering the wheat fields melts, the water seeps into the soil, and the surface layer of soil will form an ice soil layer due to the low temperature. The ice layer freezes some of the overwintering pests in the shallow soil. However, if there is no snowfall during the winter, pests will increase when the temperature picks up in spring.
The absence of snowfall also makes the air cold and dry, with dust and bacteria floating in the air, which can have a negative impact on people's health. In particular, it will accelerate the spread of respiratory viruses and easily induce respiratory diseases.
That being the case, it begs the question of whether it is feasible to use artificial snowfall. In terms of weather conditions, rain and snow formation requires a confluence of cold and warm air currents and sufficient water vapor in the clouds. There also needs to be sufficient ice nuclei in the clouds to help snow crystals coalesce and turn into snowflakes to land on the ground.
However, if there is a lack of natural ice crystals in the cloud, artificial ice nuclei need to be seeded into the cloud to promote a rapid increase in the number of ice crystals in the cloud. The main artificial ice nucleus is silver iodide, which is dispersed directly into the clouds by aircraft, rockets, ground burners, etc.
As early as the 1960s, countries such as the United States, Spain and Australia conducted long-term tests on the concentration of silver ions in the environment after silver iodide catalyzed precipitation. The results showed that the concentration of silver ions produced after artificially influenced weather was very low and had a negligible environmental impact.
Yao Zhangyu, a researcher at the China Meteorological Administration, said the weather process of artificial snow is generally a large-scale systematic snowfall weather process in which water vapor is constantly replenished from outside the clouds to inside the clouds. At the same time, the updraft is constantly changing, and the clouds themselves are constantly forming. Therefore, the artificial snow increase generally does not affect other areas.
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