HEAT WAVE / HOT DAY
During summer season the intense heating of land, spells of hot weather occurs occasionally resulting in rise of temperatures and causing human discomfort. These spell affects certain parts of India shifting one place to another. This phenomenon is called Heat Wave.
Understanding Heat Wave:
There are many cities whose normal maximum temperatures varies place to place. Heat wave is given to the places whose normal temperature is atleast 40 deg C and there is rise in temperature by 5 to 6 deg C. For example: during April Latur has normal temperature of 40 deg C and Bikaner has 43 deg C. If both stations record 45 deg C than Latur will have heat wave condition and not Bikaner.
To declare heat wave 2 or more stations should satisfy the above conditions.
Below is the conditions for declaring Heat Wave:
a) When normal maximum temperature of a station is less than or equal to 40º C
- Heat Wave Departure from normal is 5º C to 6º C
- Severe Heat Wave Departure from normal is 7º C or more
b) When normal maximum temperature of a station is more than 40º C
- Heat Wave Departure from normal is 4º C to 5º C
- Severe Heat Wave Departure from normal is 6º C or more
c) When actual maximum temperature remains 45ºC or more irrespective of normal maximum temperature, heat wave is be declared.
The hot day concept was introduced in 2002 which is related with the human discomfort caused due to to the increase of night temperature by 5 to 6 deg C and the day temperature is 40 deg C or above. Hence the night becomes more uncomfortable due to less cooling or increase in humidity.