A heat wave is defined as a prolonged period of excessively hot weather, measured in relative to the usual weather conditions and normal temperatures of a particular area. Simply it means, temperatures that people from a hotter climate consider normal can be termed as heat wave in a cooler area.
When is a heat wave declared?
Heat wave need not be considered till maximum temperature of a station reaches 40°C for plains and at least 30°C for hilly areas. On the other hand, when the actual maximum remains 45 or more irrespective of normal maximum temperature, heat wave should be declared.
When the average maximum temperature of a station for a month is less than or equal to 40°C,
a. Heat wave is declared when the departure from normal is 5°C to 6°C
b. Severe heat wave is declared when the departure from normal is 7°C or more
When the average maximum temperature of a station for a month is more than 40°C,
a. Heat wave is declared when the departure from normal is 4°C to 5°C
b. Severe heat wave is declared when the departure from normal is 6°C or more
What causes a heat wave?
Heat waves are a common phenomenon during the summer season, when the sun's rays are directly over the Indian region. With constant insulation, temperatures keep rising and in the absence of any weather activity heat waves form. Moreover, persistent hot and dry northwesterly winds blowing from the desert region add on to the rising heat.
What is the impact of a heat wave?
A heat wave is a very dangerous situation and major threat to lives. Heat waves are increasingly becoming more frequent. Even 10 years back, death toll from heat that were recorded over an entire summer are now occurring in just one week. This could be attributed to increasing urbanization. Most of the heat-related deaths go unreported and are taken to be the consequences of other existing ailments of the poor and deprived.