Heat Waves (Disaster Management)

• A heat wave refers to a period in the summer months when temperatures rise significantly above the usual maximum temperature.
• Countries declare heat waves differently. Indian Meteorological Department declares a Heatwave when
  • A departure of 4.5 to 6.4 degrees from the normal is considered a heat wave, while a departure above 6.4 degrees C is considered a severe heat wave.  
  • If the normal temperature of the station is more than 45°C (or 37°C at Hill Station), then a heat wave is to be declared irrespective.  

• Heat waves predominantly occur in India between March and June and occasionally, in rare instances, even extend into July. The month of May is the peak period for heat waves in India.

1. In North-Central India

• In North-Central India, heat waves are commonly observed during summer when an area experiences high pressure ( typically formed by Jet Streams). Heat waves occur due to trapped air caused by the downward force of high-pressure systems. This force prevents the air near the ground from rising, creating a cap-like effect that traps warm ground air in place. 
• Loo: The dry and hot westerly winds originating from Baluchistan, central Pakistan, and the Thar Desert play an important role in the occurrence of heatwaves.

2. In Coastal Areas

• Coastal areas near the Bay of Bengal frequently encounter a significant number of heat waves due to a phenomenon known as the Matsuno-Gill Response. This response occurs when the sea surface temperature of the Bay of Bengal decreases, leading to the development of low pressure over the area during summers. Consequently, the absence of sea breeze flowing from the Sea towards the land disrupts the moderating effect on the climate in coastal areas, resulting in the formation of heat waves.

3. In Cities

• Urban areas experience the Urban Heat Island Effect, where cities tend to become hotter due to an abundance of cement and concrete and a lack of tree cover. This effect exacerbates the situation by causing ambient temperatures to feel 3 to 4 degrees Celsius higher than they actually are.

4. Green House Gas (GHG)

• GHGs contribute to the retention of heat in the Earth’s atmosphere. A stronger greenhouse effect reduces the amount of heat radiation from the Earth that can escape into space.

• Heat Stroke and Heat Exhaustion: Heat waves pose a significant risk of heat stroke and heat exhaustion. 
  • Heat stroke occurs when there is continuous and prolonged exposure to high temperatures, leading to symptoms such as nausea and heat cramps. This condition can result in a rapid rise in body temperature, which can be life-threatening if not treated promptly. 
  • Heat exhaustion, on the other hand, is caused by dehydration due to excessive sweating and inadequate water intake during hot weather.
• Risk of Wildfires: Prolonged heat waves can increase the risk of wildfires. As the heat wave continues, the lack of moisture in the environment dries out vegetation, creating ideal conditions for the ignition and spread of forest or brush fires.
• Drought Conditions: Heat waves exacerbate drought conditions. Soaring temperatures during the dry season intensify the impact of water scarcity, affecting millions of people. 
• Prevents Cloud Formation: Heat waves can hinder cloud formation. The hot and dry conditions suppress the formation of clouds, reducing the chances of rainfall. 
• Impacts on Outdoor Workers: Heat waves severely threaten outdoor workers, particularly labourers and poor farmers who have no choice but to work in blistering conditions. These individuals are at a higher risk of heat-related illnesses and fatalities due to prolonged exposure to extreme heat.
• Increased Energy Demands: Sweltering heat waves lead to a surge in energy demand, particularly electricity