We have likely heard the terms “severe cold” and “harmful cold” in weather reports, but have you ever wondered about the differences between these two concepts? If so, let’s explore this topic in detail through the article below.
In fact, distinguishing between these two concepts is quite simple; the most fundamental difference lies in the average daily temperature, specifically:
- Cold weather occurs when the average daily temperature in the area typically ranges from 20 to 22 degrees Celsius.
- Severe cold: When the average daily temperature in the area typically ranges from 15 to 20 degrees Celsius.
- Very severe cold is when the average daily temperature in the area typically ranges from 13 to 15 degrees Celsius.
- Harmful cold is when the average daily temperature in the area drops below 13 degrees Celsius (There are two types of harmful cold that we will discuss in detail at the end of this article).
These two phenomena are primarily used for the lowland and midland regions of Northern Vietnam and the North Central region, and these terms do not apply to mountainous areas (the reason being that these phenomena occur almost throughout the month in mountainous areas rather than in bursts).
For instance, in Sapa (Lao Cai), severe cold occurs almost throughout December, January, and February.
So why is it important to distinguish between “very severe cold” and “harmful cold”?
The reason these two concepts are clearly separated is that in Northern Vietnam, rice production is the primary food crop, and this is where most agricultural activities take place during the cold season.
Thus, the terms “very severe cold” and “harmful cold” are mainly used in the field of agriculture to help farmers adopt appropriate measures to cope with this extreme weather phenomenon and to understand the impact it has on their crops.
Scientists have studied and calculated the impact of average daily temperatures on the photosynthesis capacity of plants, which forms the basis for categorizing them into the two levels mentioned above.
If severe or harmful cold lasts for only one day, the photosynthesis and growth of plants remain normal. However, if it extends for two days or more, it can weaken the plants’ resistance and lead to death due to their inability to photosynthesize and protect themselves.
Another important point to note is that “very severe cold” and “harmful cold” must be accompanied by overcast weather, cloudy conditions, and possibly light rain (otherwise, it will not be classified as very severe or harmful cold even if the average daily temperature drops to 15 or 13 degrees Celsius).
Classification of common cold types. (Photo: Thanh Luan).
Additionally, according to Mr. Le Thanh Hai, former Director of the National Center for Meteorological and Hydrological Forecasting, on Science and Life, harmful cold can be divided into two distinct types: Dry severe cold and humid severe cold.
- Among them, humid severe cold is characterized by numbness and tingling in the extremities, with very high humidity (80 to 90%), temperatures around 10 degrees Celsius accompanied by rain or even snowfall in high mountain regions, where the indoor and outdoor temperatures are not significantly different.
- Dry severe cold can be even more uncomfortable, with air temperatures dropping to 7 – 9 degrees Celsius, humidity at 20 – 30%, but without rain or even sunshine during the day. At night, frost and ice may occur in mountainous areas, and the temperature indoors is slightly warmer than outside.
Another common rule is that if dry severe or harmful cold occurs in the first half of the season, then humid severe cold will occur in the second half. Thus, among the common types of cold, dry cold is the ‘most feared’ due to extremely low temperatures (7 to 9 degrees Celsius).
