Cold wave: A rapid fall in temperature within 24 hours to a level requiring substantially increased protection to agriculture, industry, commerce, and social activities.

Derecho: “a widespread, long-lived, straight-line windstorm (no rotation like a tornado)” that is associated with a “band of rapidly moving showers or thunderstorms”.

The name comes from the Spanish word ‘la derecha’ which means ‘straight’.

It is a warm-weather phenomenon that generally occurs in June and July.

Analysis period of 1971-2010:  Cold wave/ Severe cold wave spells are 1-2 days, but in some cases, it lasted for 10 days. There are more than an average of 6 cold wave days in the period.

• India’s ‘core cold wave zone’ covers Punjab, Himachal Pradesh, Uttarakhand, Delhi, Haryana, Rajasthan, Uttar Pradesh, Gujarat, Madhya Pradesh, Chhattisgarh, Bihar, Jharkhand, West Bengal, Odisha and Telangana.

Nodal Ministry: Min. of Agriculture and Farmers Welfare (MAFW)

Cold Wave Types

1. Advection Cold Wave: This occurs when cold air moves into an area, lowering temperatures. An example is the Siberian cold wave in Europe during winter.
2. Radiation Cold Wave: This happens under clear skies with calm winds, allowing heat to radiate away at night. An example is a clear winter night in the northern United States.
3. Frontal Cold Wave: Results from the passage of a cold front, causing a sudden drop in temperature. Example: A cold front moving through during a thunderstorm.

Criteria to Declare:

If the Wind chill factor (a measure of the cooling effect of the wind on the temperature of the air)

is 10°C or less, then only the conditions for cold waves are considered.

• For the plains: When the minimum temperature is 10 degrees Celsius or below and is 4.5 to 5.5 degrees Celsius (C) less than normal for two consecutive days. A severe cold wave is declared when the temperature deviation from normal is -6 to -7 degrees Celsius. When the Wind chill factor is 0°C or less, the Cold Wave should be declared irrespectively.
• For coastal stations: The threshold value of a minimum temperature of 10 degrees Celsius is rarely reached. However, the local people feel discomfort due to the wind chill factor which reduces the minimum temperature by a few degrees depending upon the wind speed.

Causes:

• Cold wave:
  1. Absence of cloud cover in the region: Clouds trap some of the outgoing infrared radiation and radiate it back downward, warming the ground.
  2. Snowfall in the upper Himalayas has blown cold winds towards the region.
  3. Subsidence of cold air over the region: Subsidence is the downward movement of cold and dry air closer to the surface.
  4. Prevailing weak La Nina conditions in the Pacific Ocean.
  5. La Nina is the abnormally cooler sea surface temperature reported along the equatorial Pacific Ocean and it is known to favor cold waves.
  6. During La Nina years, the severity of cold conditions becomes intense. The frequency and area covered under the grip of a cold wave become larger.
• Derechos:
  1. Heat and Moisture: Associated with warm, moist air masses, often develop in the warm sector of a rapidly moving low-pressure system.
  2. Atmospheric Instability: Derechos require atmospheric instability, which is characterized by rising warm air and falling cool air.
  3. Squall Line: Derechos are a type of severe windstorm associated with a long-lived squall line of severe thunderstorms.
  4. Downbursts: Within the squall line, downbursts are powerful & can create straight-line wind damage over a wide area.
  5. High Wind Gusts: Derechos are known for their destructive straight-line wind gusts, which can exceed 58 miles per hour (93 kilometers per hour) and are often associated with widespread wind damage.

Mitigation:

1. Shelter and Relief Camps: Setting up temporary shelters and relief camps to provide warmth, food, and medical assistance.
2. Winter Clothing Distribution: Distributing warm clothing, blankets, and winter essentials to communities in need.
3. Weather Forecasting and Early Warning Systems: Improving weather forecasting capabilities and disseminating timely cold wave warnings to the public.
4. Community Awareness Programs: Educate people about the risks of cold waves and the importance of staying warm, along with tips for winter safety.
5. Heating Facilities: Installing heating facilities in public spaces, like community centers, schools, and hospitals.
6. Power Supply Maintenance: Ensuring the reliability of power supply during cold waves to avoid disruptions in heating systems and essential services.
7. Social Support Programs: Providing financial assistance and support to vulnerable populations.
8. Coordination with NGOs and International Agencies: Collaborating with non-governmental organizations (NGOs) and international agencies to enhance the reach and effectiveness of cold wave mitigation efforts.

Way Forward:

Cold Wave: Improve winter preparedness, provide shelter for vulnerable populations, and ensure access to heating resources in affected areas. Address climate change to reduce the frequency and severity of cold waves.

Derecho: Enhance early warning systems for severe thunderstorms, strengthen infrastructure against high winds, and educate the public on derecho risks. Foster regional cooperation for effective response to widespread derecho events.

The IPCC defines heatwave as “a period of abnormally hot weather, often defined with reference to a relative temperature threshold, lasting from two days to months.”

• Heatwaves Duration Index & World Meteorological Organization— A heat wave occurs when the daily maximum temperature of more than five consecutive days exceeds the average maximum temperature by 5 °C (9 °F).
• Heatwaves typically occur between March and June, more frequently over the Indo-Gangetic plains, on average, 5-6 heat wave events occur every year over the northern parts of the country.
• Heat cramps: Edelman (Swelling) and syncope (Fainting) are generally accompanied by fever below 39 degrees Celsius.
• Heat Exhaustion: Fatigue, weakness, dizziness, headache, nausea, vomiting, muscle cramps, and sweating.
• Heat stroke: Body temperature is at 40°C or more along with delirium, seizures, or coma which is potentially fatal.
• Heat waves are more frequent over the Indo-Gangec plains of India. On average, 5-6 heat wave events occur every year over the northern parts of the country.

Nodal Ministry: Indian Meteorological Department (Ministry of Earth Sciences, MOES)

Types of HeatWaves:

1. Moderate Heatwave: A heatwave with temperatures exceeding the normal maximum by 3-5°C. Example: A moderate heatwave in Delhi with temperatures reaching 42°C (108°F) in May.
2. Severe Heatwave: More intense than moderate heat waves, with temperatures exceeding the normal maximum by over 5°C. Example: A severe heatwave in Rajasthan with temperatures soaring to 50°C (122°F) in June.
3. Sustained Heatwave: A prolonged period of high temperatures lasting for several days. Example: A sustained heatwave in Odisha lasting for a week with temperatures consistently above 40°C (104°F).
4. Heatwave with High Humidity: Occurs when high humidity levels make it feel even hotter. Example: A humid heatwave in Mumbai with temperatures in the high 30s°C (around 100°F) and high humidity levels.

Criteria to declare:

1. Heatwave: When the maximum temperature of a met-substation reaches at least 40°C (104°F) in the plains or 37 degrees or more in coastal areas, 30°C (86°F) in hilly areas
2. Severe Heatwave: When the maximum temperature of a met substation reaches at least 45°C (113°F) in the plains or 30°C (86°F) in hilly regions.

Causes:

Heatwaves in India can be caused by various factors, including:

1. High Temperatures: India’s geographical location and topography make it susceptible to intense heat.
2. Seasonal Weather Patterns: The movement of weather systems, such as the Indian Ocean Dipole and El Niño, can influence temperature and precipitation patterns, contributing to heat waves.
3. Lack of Rainfall: Prolonged periods of low rainfall, or droughts, lead to soil moisture depletion and less evaporative cooling.
4. Urban Heat Island Effect: Urban areas with concrete and asphalt can absorb and retain heat, causing localized temperature increases. Rapid urbanization contributes to this effect.
5. Global Climate Change: Long-term changes in global climate patterns can result in more frequent and severe heat waves.
6. Wind Patterns: Changes in wind patterns can influence the movement of air masses, potentially trapping warm air and causing prolonged periods of extreme heat.
7. Monsoon Delay or Failure: The delay or failure of the monsoon contributes to heat waves.
8. Deforestation and Land Use Changes: Alterations in land cover, leading to higher temperatures.
9. Human Activities: Activities like industrial processes, transportation, and agriculture can release heat-trapping gases and pollutants, contributing to local warming.

Mitigation:

1. Early Warning Systems: Implement advanced meteorological forecasting systems to provide early warnings about impending heatwaves.
2. Cooling Centers: Establish cooling centers in urban areas where vulnerable populations can seek refuge during extreme heat events.
3. Urban Planning: Design and retrofit urban areas to reduce the urban heat island effect.
4. Building Design: Promote energy-efficient building designs incorporating natural cooling techniques, such as proper ventilation, insulation, and shading.
5. Public Awareness: Educate people about the risks of heat waves and the importance of staying hydrated, wearing appropriate clothing, and avoiding outdoor activities during peak heat hours.
6. Water Supply: Ensure stable and reliable access to clean water as it is crucial for hydration and cooling.
7. Healthcare Preparedness: Train healthcare workers to recognize and treat heat-related illnesses promptly.
8. Heat-Related Research: Invest in research to better understand local climate patterns, heatwave dynamics, and vulnerability assessments to tailor mitigation efforts effectively.
9. Reducing Greenhouse Gas Emissions: As a long-term strategy, work towards reducing greenhouse gas emissions to mitigate the effects of global climate change.
10. Adaptive Agriculture: Promote climate-resilient agricultural practices to reduce the impact of heatwaves on food production and farmers.
11. Heat-Resilient Construction: Encourage the construction of buildings and infrastructure that can withstand extreme heat conditions.

NDMA Guidelines:

• You think someone is suffering from the heat:
  1. Move the person to a cool place under the shade
  2. Give water or a rehydrating drink (if the person is still conscious)
  3. Fan the person
  4. Consult a doctor if symptoms get worse or are long-lasting or if the person is unconscious
  5. Do not give alcohol, caffeine, or aerated drink
  6. Cool the person by putting a cool wet cloth on his/her face/body
  7. Loosen clothes for better ventilation
• Emergency Kit
  1. Water bottle
  2. Umbrella/ Hat or Cap / Head Cover
  3. Hand Towel
  4. Hand Fan
  5. Electrolyte / Glucose / Oral Rehydration

Way Forward:

1. The National Action Plan for Climate Change (NAPCC) should be implemented in true spirit for inclusive growth and ecological sustainability.
2. Nature-based solutions should be considered, not just for tackling climate change-induced heat waves but also for doing so ethically and promoting intergenerational justice.
3. Sustainable Cooling
4. Passive cooling technology, a widely-used strategy to create naturally ventilated buildings, can be a vital alternative to address the urban heat island for residential and commercial buildings.
5. The Intergovernmental Panel on Climate Change (IPCC) in the third part of its AR6 stated that ancient Indian building designs that have used this technology, can be adapted to modern facilities in the context of global warming.