The India Meteorological Department (IMD) has warned of another year of extreme heat and above-normal heatwaves. This comes as Delhi recorded its hottest February in 74 years and Mumbai faced two heatwaves even before mid-March.

Heatwaves in India are becoming more severe and frequent, posing serious health risks. IMD predicts a rise in maximum temperatures and more heatwaves in eastern and southern India in the coming days. India must stay prepared to handle these recurring heatwaves.

About Heatwaves

Heatwaves- Heat waves are prolonged periods of excessively hot weather that can cause adverse impacts on human health, the environment, and the economy.

Definition of Heatwave- In India IMD defines heatwave based on the following criteria.

Physiography of regions

• Plain– The maximum temperature recorded at a station is 40 degrees Celsius or more.
• Coast- The maximum temperature recorded at a station is 37 degrees Celsius or more.
• Hills- The maximum temperature recorded at a station is 30 degrees Celsius or more.

Based on Departure from Normal Temperature

• 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

• Heat Wave- When actual maximum temperature ≥ 45°C 
• Severe Heat Wave- When actual maximum temperature ≥47°C 

(*Heat Wave is declared if above criteria are met in at least 2 stations in a Meteorological subdivision for at least two consecutive days.)

Status of Heatwaves in India

India has been affected by the Heatwaves since a long time. However, during the last few decades, due to increased instances of climate change, the impact of heat waves has also enhanced quite significantly.

1. States like Rajasthan, Gujarat, Uttar Pradesh, Delhi, Haryana, Punjab, Madhya Pradesh have been affected the most by the Heatwaves.
2. According to IMD, between 1981 and 1990 there were 413 heatwave days in India. However, the heatwave days have increased to 600 days between 2011 and 2020.
3. The number of deaths from heat-related causes increased from 5,457 between 1981 and 1990 to 11,555 between 2011 and 2020.

Causes of heatwaves in India

Heatwaves in India are driven by a mix of natural and human-induced factors. Let’s break them down in simple terms:

Natural Causes:

1. Trapped Hot Air – Sometimes, a high-pressure system stalls over a region, acting like a lid that traps hot air near the surface. With no airflow to disperse the heat, the temperature keeps rising. (Example: The 2015 heatwave in Telangana and Andhra Pradesh, which killed over 2,000 people, was worsened by a stalled high-pressure system.)
2. El Niño & Climate Variability – Events like El Niño disrupt weather patterns, making some areas drier and hotter than usual. (Example: In 2019, an El Niño event led to higher-than-normal temperatures across India, worsening heatwaves.)
3. Drought & Dry Land – When there’s little rain, the soil loses moisture, making it easier for the land to heat up. Dry land absorbs and retains heat more than moist soil. (Example: Rajasthan and Gujarat often face severe heatwaves due to prolonged dry spells.)
4. Hot Winds & Shifting Patterns – Winds can carry hot air from one place to another, worsening heat conditions in areas that aren’t usually this hot. (Example: In North India, hot ‘Loo’ winds from the Thar Desert increase summer temperatures dramatically.)
5. Geography Matters – Some areas are naturally prone to heatwaves due to their location. Landlocked valleys and cities surrounded by mountains trap heat, making the temperatures rise even more. (Example: Delhi’s location between the Thar Desert and the Himalayas makes it prone to extreme heat.)

Human-Induced Causes:

1. Climate Change & Global Warming – Human activities like burning fossil fuels, deforestation, and industrial pollution have increased global temperatures, making heatwaves more frequent and severe. (Example: In the last century, India’s average temperature has risen by nearly 0.7°C, making summers hotter.)
2. Urban Heat Island Effect – Cities filled with concrete buildings, asphalt roads, and fewer trees absorb and retain heat, making them much hotter than surrounding rural areas. (Example: Mumbai and Delhi often experience temperatures 3-5°C higher than nearby villages due to the urban heat island effect.)
3. Deforestation & Loss of Green Cover – Trees and forests naturally cool the environment by providing shade and releasing moisture into the air. Large-scale deforestation for agriculture, urban expansion, and infrastructure projects has reduced this cooling effect, making temperatures rise.
   Example: The loss of forests in Chhattisgarh and Jharkhand for mining has led to rising local temperatures and more frequent heatwaves.
4. Air Pollution & Heat-Trapping Gases – Industrial emissions, vehicle exhaust, and burning crop residues release greenhouse gases and pollutants that trap heat in the atmosphere, worsening global warming.
   Example: The thick smog over Delhi in summer doesn’t just cause breathing issues—it also contributes to trapping heat, making heatwaves last longer.
5. Overuse of Air Conditioners & Cooling Systems – Ironically, while ACs cool indoor spaces, they release heat into the outside environment, increasing temperatures in cities. The more people use cooling systems, the hotter it gets outside.
   Example: Cities like Hyderabad and Bengaluru, once known for their moderate climate, now experience hotter summers due to increased AC usage and rapid urbanization.

In short, while natural weather patterns do play a role, human activities have made heatwaves worse and more common. Addressing climate change and improving urban planning are key to reducing their impact.

Impact of heatwaves in India

1. Danger to Human Health – When temperatures rise too fast, our bodies struggle to cool down, leading to heat cramps, exhaustion, heatstroke, and even fatal conditions like hyperthermia. The elderly, children, and outdoor workers are the most vulnerable.
   Example: In 2023, India recorded over 200 deaths due to heatstroke, especially in states like Uttar Pradesh and Bihar.
2. Strain on Electricity & Power Supply – As people crank up their air conditioners and fans, electricity demand surges, often pushing power grids to the brink of collapse, causing blackouts.
   Example: During Delhi’s extreme heatwaves, power cuts leave people struggling without cooling, worsening the crisis.
3. Economic Losses & Reduced Productivity – Heatwaves slow down work, especially in outdoor jobs like farming, construction, and factory work. Workers lose energy faster, and businesses see a drop in efficiency.
   Example: A study by the International Labour Organization (ILO) found that at 34°C, workers lose up to 50% of their work capacity, leading to massive economic losses.
4. Water Shortages & Conflicts – Extreme heat causes rivers, lakes, and reservoirs to dry up, worsening India’s already severe water crisis. This often leads to disputes between states over water-sharing.
   Example: The Cauvery Water Dispute between Karnataka and Tamil Nadu intensifies during heatwaves due to reduced river flow.
5. Threat to Food Security – Higher temperatures increase the risk of droughts, making it harder for crops to grow. Farmers need more irrigation water, which further strains water resources. This results in lower yields and rising food prices.
   Example: In 2022, wheat production in North India dropped significantly due to an unexpected heatwave, driving up wheat prices nationwide.

HEATWAVE MANAGEMENT STRATEGY IN INDIA

Way forward: Mitigation measures that can be taken 

• Providing cool shelters: Similar to cyclone and disaster relief centres, public cooling centres can be built where people can go to cool off during extreme heat.
  • The concept has been explored in Barcelona, Paris and Rotterdam among others. 
• Improving the built environment: By making them more heat-resilient through the incorporation of better insulation and ventilation systems in buildings, planting more trees etc.
• Utilising indigenous knowledge: Usage of indigenous protective methods against heat waves and strokes must be tapped, documented, and researched.
• Inclusion of regulative provisions: For example, making it mandatory for components like passive ventilation and cool roof technologies in the Building bylaws to increase thermal comfort.
• Capacity building for health care professionals: at the local level to recognize and respond to heat-related illnesses.

#BACK2BASICS : 

OTHER DECLARATIONS BY IMD: 

• Marine Heatwaves (MHW): It is defined when seawater temperatures exceed a seasonally-varying threshold (usually the 90th percentile) for at least 5 consecutive days.
  • MHWs have increased by up to four-fold in the tropical Indian Ocean, aided by rapid warming in the Indian Ocean and strong El Niños.
• A warm night: It’s declared only when the maximum temperature remains 40°C or more. It is defined based on departures of actual minimum temperatures as follows:
  • Warm night: minimum temperature departure is 4.5°C to 6.4°C
  • Very warm night: minimum temperature departure is >6.4°C.
• Hot and Humid Weather: When observed maximum temperatures over any station remains 3°C above normal along with the above normal relative humidity, it is termed as Hot & Humid Weather over that station.

NDMA GUIDELINES ON HEATWAVES

• Avoid going out in the sun, especially between 12.00 noon and 3.00 p.m.
• Drink sufficient water as often as possible.
• Wear lightweight, light-coloured, loose, and porous cotton clothes. Use protective goggles, an umbrella/hat, shoes or chappals while going out in sun.
• Avoid alcohol, tea, coffee and carbonated soft drinks, which dehydrate the body.
• Avoid high-protein food and do not eat stale food.
• Use ORS, homemade drinks like lassi, torani (rice water), lemon water, buttermilk, etc. which helps to rehydrate the body.
• Keep animals in the shade and give them plenty of water to drink.
• Keep your home cool, use curtains, shutters or sunshade and open windows at night.
• Use fans, damp clothing and take bath in cold water frequently.

Heat Action Plan

• A Heat Action Plan (HAP) is a comprehensive strategy developed by governments or organisations to mitigate the health risks associated with extreme heat events.
  • It includes measures to protect vulnerable populations, provide information and resources, and coordinate responses during heatwaves.
• They outline short-term measures, including alerts and inter-departmental coordination, to reduce human casualties. HAPs entail long-term strategies like infrastructure upgrades such as cool roofs and enhanced greenery to prepare for future heat waves based on data analysis.
• Odisha first developed a Heat Action Plan in 1999 following more than 2,000 Heat Wave deaths in 1998. Following this, the first city-level Action Plan was developed by Ahmedabad in 2013 following the severe Heat Wave in 2010.
• The NDMA and IMD are working with 23 States to develop HAPs. There is no centralised database on HAPs, but at least 23 HAPs exist at the State and city level, with a few States, such as Odisha and Maharashtra, laying out district-level HAPs.