In recent years, heat waves and heat domes have become more frequent and severe due to climate change.
HEAT WAVE
- A Heat Wave is a period of abnormally high temperatures, more than the normal maximum temperature that occurs during the summer season in the North-Western parts of India.
- Heat Waves typically occur between March and June, and in some rare cases even extend till July.
Extreme temperatures and resultant atmospheric conditions adversely affect people living in these regions as they cause physiological stress, sometimes resulting in death.
CRITERIA FOR HEAT WAVE
IMD has given the following criteria for Heat Waves:
Two conditions which need to be satisfied:
- Heat wave is considered if maximum temperature of a station reaches at least 40°C or more for Plains, 37°C or more for coastal stations and at least 30°C or more for Hilly regions. Following criteria are used to declare heat wave:
- Based on Departure from Normal
- Heat Wave: Departure from normal is 4.5°C to 6.4°C
- Severe Heat Wave: Departure from normal is 6.4°C
- Based on Actual Maximum Temperature (for plains only)
- Heat Wave: When actual maximum temperature 45°C
- Severe Heat Wave: When actual maximum temperature 47°C
To declare heat wave, above criteria should be met at least in 2 stations in a Meteorological subdivision for at least two consecutive days.
FAVOURABLE CONDITIONS FOR HEAT WAVE
- Transportation/Prevalence of hot dry air over a region (There should be a region of warm dry air and appropriate flow pattern for transporting hot air over the region).
- Absence of moisture in upper atmosphere (As presence of moisture restricts the temperature rise).
- Sky should be cloudless (To allow maximum insulation over the region).
- Large amplitude anti-cyclonic flow over the area.
- Heat waves develop over Northwest India and spread gradually eastwards & southwards but not westwards (since the prevailing winds during the season are westerly to north westerly).
But on some occasions, heat wave may also develop over any region in situ under the favourable conditions.
Impacts of Heat Waves
- Health Impacts: Health impacts of Heat Waves typically involve dehydration, heat cramps, heat exhaustion and/or heat stroke. The signs and symptoms are as follows:
- Heat Cramps: Ederna (swelling) and Syncope (Fainting) accompanied by fever below 39 i.e.,102*F.
- Heat Exhaustion: Fatigue, weakness, dizziness, headache, nausea, vomiting, muscle cramps and sweating.
- Heat Stoke: Body temperatures of 40*C i.e., 104*F or more along with delirium, seizures or coma. This is a potentially fatal condition.
- Agriculture:
- High temperatures can be damaging to agriculture. Plant growth is negatively impacted by high daytime temperatures and some crops require cool night temperatures.
- Heat waves also increase the chances of livestock experiencing heat stress, especially when night-time temperatures remain high, and animals are unable to cool off.
- Heat-stressed cattle can experience declines in milk production, slower growth, and reduced conception rates.
- Heat waves can exacerbate droughts and wildfires, which can lead to negative impacts on the agriculture sector.
- Energy: Warmer temperatures affect many aspects of energy system, including production, transmission, and demand. While higher summer temperatures increase electricity demand for cooling, at the same time, they can lower the ability of transmission lines to carry power, leading to electricity reliability issues like rolling blackouts during heat waves.
In the ultimate analysis, we have no option but reduce the emission of greenhouse gases to tackle the climate crisis. But till a lasting solution is found, it is important to roll out heat action plans in regions vulnerable to heatwaves. Mitigation is of immediate concern regarding high summer temperatures and subsequent heatwaves. Both short term measures like advisories and long-term measures like afforestation must be simultaneously acted upon.
High-pressure circulation in the atmosphere acts like a dome or cap, trapping heat at the surface and favoring the formation of a heat wave.
A heat dome is caused when atmosphere traps hot ocean air, as if bounded by a lid or cap. They can be linked to climate change. The upper air weather patterns are slow to move referred to by meteorologists as an Omega block.
In still, dry summer conditions, a mass of warm air builds up. The high pressure from the Earth's atmosphere pushes the warm air down. The air is compressed, and as its net heat is now in a smaller volume, so it must get hotter. As the warm air attempts to rise, the high pressure above it forces it down, to get hotter, and its pressure grows higher.
The high pressure acts as if a dome, causing everything below it to get hotter and hotter.