Heat Wave Vs Cold Wave: According to the India Meteorological Department (IMD), India recorded 99 days of cold waves in 2020. Also, the report showed that nearly 2.7 times there has been an increase in the number of cold wave days from 2017-2020. From 1980-2018, cold waves killed more Indians than heat waves. It has been reported that the number of cold wave days has been consistently on the rise since 2017.
As per the WHO, the most common causes of death associated with cold waves include coronary heart disease, cerebrovascular accidents, and respiratory diseases. IMD said that the average monthly minimum temperature over northwest India in January 2021 has been lower than that of 2019 and 2020.
What is a Cold Wave?
In some regions, a cold wave is known as a cold snap or cold spell. It is a weather phenomenon associated with the cooling of the air. According to the U.S. National Weather Service, "Cold wave is defined as a rapid fall in temperature within a 24-hour period and required substantially increased protection to agriculture, industry, commerce, and social activities."
The criteria or basis for a cold wave are the rates at which the temperature falls, and the minimum to which it falls. Here to know is that the minimum temperature is dependent on the geographical region and time of year. A cold wave of sufficient magnitude and duration may be defined as a cold air outbreak (CAO).
What is a Heat Wave?
It is a weather phenomenon when an abnormal temperature rises in a period more than the normal maximum temperatures that occur during the summer season.
According to World Meteorological Organisation, a heat wave is defined as five or more consecutive days of prolonged heat in which the daily maximum temperature is higher than the average maximum temperature by 5 degrees Celsius or more.
Difference between Heat and Cold Wave
| Reasons | Heat Wave | Cold Wave |
| Definition | Period of prolonged, abnormally high surface temperatures relative to those normally expected. It may span from several days to several weeks. | Cold Wave is a speedy fall in temperature over a 24-hour period that requires considerably enhanced protection for agriculture, industry, commerce, and social activities. |
| Criteria | When the maximum temperature of a region increases by at least 40 degrees Celsius for Plains and at least 30 degrees Celsius for Hilly regions. According to IMD, For five or more consecutive days during which the daily maximum temperature surpasses the average maximum temperature by 5 degrees Celsius or more. | When the minimum temperature is 10 degrees Celsius or below and is 4.5 degrees Celsius less than normal for two consecutive days. |
| Regions in India | Hot weather is experienced in certain parts of India during the months of March to July. | Cold and dry winds blow in northwest India during the months of November and April. |
| Health Impacts | Dehydration, heat cramps, heat exhaustion, and heatstroke. It also causes weakness, dizziness, headache nausea, muscle cramps, and sweating. People living in extreme temperatures and resultant atmospheric conditions may cause physiological stress and sometimes result in death. | Prolonged exposure to cold wave conditions, lowers the temperature of the body as the body loses heat faster than it can produce by muscle contractions, metabolism, and shivering. Illness related to coldwaves is frostnip, chilblains, frostbite, etc. |
| Prevention | One of the best ways to prevent illness due to heat waves is to avoid prolonged exposure to the outdoor environment. Wear light-weight, light colour clothes which can absorb sweat from the skin, wear clothes with loose fittings which allow more air circulation; cover the head with a well-ventilated cap or hat while going outside in hot sunny weather, avoid dehydration, etc. | Avoid prolonged exposure to the outdoor environment, dress clothes that retain body warmth and help minimise loss of heat, protect eyes from cold and wind by wearing glasses, maintain body heat by eating proper food, avoid touching metal mainly with wet hands as it can cause frost-bite in case of extreme cold temperatures. It is suggested that not to drink beverages that contain alcohol or caffeine and do not smoke tobacco as it is harmful to the lungs. |
| Phenomenon | El Nino (warm phase). During El Nino, surface winds across the entire tropical Pacific are weaker than usual. Ocean temperatures in the central and eastern tropical Pacific Ocean are warmer than average. | La Nina (cold phase). In this, the surface winds across the entire tropical Pacific are stronger than usual, and most of the tropical Pacific Ocean is cooler than average. |
Therefore, we can say that the severity and the frequency of occurrence of cold and heat waves depend upon several factors including the geographical location, climatic conditions of the region, etc. It has been seen that heat and cold wave conditions cause thermal stress to the human body that may lead to various health problems and even a threat to life. These also have an adverse impact on agriculture and industrial production. In various countries, heat and cold waves account for more deaths than any other natural disaster.
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