Heat and Cold Waves in India: Climate Extremes and Health Impacts

India faces recurring climate extremes that pose serious threats to public health and livelihoods. Heat waves during summer months and cold waves in winter have become increasingly significant concerns, with both phenomena causing substantial mortality and socioeconomic disruption across the country. Understanding these temperature extremes is essential for developing effective disaster preparedness strategies and protecting vulnerable populations.

Heat waves: When temperatures cross dangerous thresholds
Geographic distribution and timing
The deadly toll of extreme heat
Underreporting and actual burden
Cold waves: The silent winter threat
Vulnerable regions and populations
Health impacts of extreme cold
Cardiovascular and respiratory stress
Broader socioeconomic impacts
Climate change and future projections

Heat waves: When temperatures cross dangerous thresholds

A heat wave represents an extended period of abnormally high temperatures that significantly exceed normal maximum temperatures. In India, these events primarily affect northwestern regions between March and June, though they sometimes persist into July. The India Meteorological Department has established specific criteria for declaring heat wave conditions based on both absolute temperatures and departures from normal values.

According to IMD guidelines, heat waves are declared when maximum temperatures reach at least 40°C for plains, 37°C for coastal stations, and 30°C for hilly regions. The classification system recognizes two levels of intensity. A moderate heat wave occurs when temperatures are 5-6°C above normal, while a severe heat wave is declared when the departure reaches 7°C or more. Any temperature of 45°C or higher qualifies as a heat wave regardless of normal patterns.

Geographic distribution and timing

Heat waves predominantly affect Punjab, Haryana, Delhi, Uttar Pradesh, Bihar, Jharkhand, West Bengal, Odisha, Madhya Pradesh, Rajasthan, Gujarat, parts of Maharashtra and Karnataka, Andhra Pradesh, and Telangana. The peak month for heat wave occurrence is May, when atmospheric conditions combine with limited pre-monsoon rainfall to create dangerously hot conditions across large portions of the country.

The deadly toll of extreme heat

Climate change has intensified heat waves globally, and India experiences more frequent and severe episodes each year. These extreme heat events cause devastating health consequences including dehydration, heat cramps, heat exhaustion, and heat stroke. The physiological stress from sustained high temperatures can overwhelm the body’s cooling mechanisms, leading to organ failure and death in severe cases.

Mortality data reveals alarming fluctuations in heat-related deaths. According to government figures, particularly deadly years include 2015 with 2,081 deaths, 2012 with 729 deaths, and 2013 with 1,433 deaths. The 2015 heat wave, which affected Andhra Pradesh and Telangana most severely, remains the deadliest since 1979. More recent data shows 510 deaths in 2016 and 505 deaths in 2019.

Underreporting and actual burden

However, recent research suggests these official figures significantly underestimate the true death toll. A comprehensive study estimates that a single five-day heat wave leads to approximately 30,000 excess deaths distributed across rural and urban districts. The actual annual burden may exceed 150,000 deaths each summer when accounting for multiple heat wave events.

Many heat-related deaths go unrecognized or are misclassified because physicians often record only the immediate medical cause on death certificates without acknowledging heat as the underlying trigger. This serious underestimation leads to misallocation of resources and inadequate preparedness measures.

Cold waves: The silent winter threat

While heat waves dominate public attention, cold waves present an equally serious hazard, particularly in northern India. A cold wave brings significant air cooling and unusually low temperatures, creating conditions that threaten human health, agriculture, and infrastructure. These recurrent winter events bring freezing conditions and serious health risks, with hundreds of annual fatalities, particularly among economically disadvantaged populations in northern urban areas.

According to IMD criteria, for plains, a cold wave is declared when the minimum temperature drops to 10°C or below and is 4.5°C less than normal for two consecutive days. A severe cold wave occurs when the departure reaches 6.4°C or more, or when actual minimum temperatures fall to 4°C or below. For coastal stations, cold wave conditions are described when minimum temperature departure is 4.5°C or less from normal and the actual minimum temperature is 15°C or less.

Vulnerable regions and populations

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. Research spanning 1978-2014 revealed that Bihar and Uttar Pradesh together account for approximately 75% of total cold wave mortalities, with Bihar alone experiencing an average of 43 deaths per cold wave event.

Health impacts of extreme cold

Cold waves can cause severe temperature drops leading to frost formation, icy conditions, and extended freezing periods. These conditions increase risks of hypothermia, frostbite, and respiratory illnesses among vulnerable groups including the homeless, elderly, children, and those in substandard housing. When body temperature drops significantly, individuals may experience progressive symptoms from shivering and difficulty speaking to sleepiness, stiff muscles, and eventually loss of consciousness.

Recent studies found that 15,000 people died from cold exposure in India over a 19-year period, with an upward trend in mortality. The risk of hypothermia and frostbite increases dramatically during cold waves, especially for vulnerable groups. Interestingly, while average winter temperatures are increasing, some parts of India are experiencing new temperature lows, affecting regions unaccustomed to extreme cold and lacking adequate protective measures.

Cardiovascular and respiratory stress

Cold temperatures make it harder to maintain internal body temperature, leading to cardiovascular stress due to vasoconstriction, where blood vessels narrow to conserve heat. This increased strain on the heart can trigger cardiac events in susceptible individuals. Cold air also irritates airways and can exacerbate respiratory conditions like asthma and chronic obstructive pulmonary disease.

Broader socioeconomic impacts

Beyond immediate health concerns, both heat and cold waves disrupt multiple sectors. Transportation systems face challenges during extreme temperatures, with heat potentially affecting aircraft operations and cold causing visibility issues due to fog. Power infrastructure experiences surges in demand as people seek heating or cooling, sometimes leading to outages.

Agriculture bears significant impacts from both extremes. Heat waves can cause crop failure through excessive evapotranspiration and stress on standing crops, while cold waves damage winter crops and horticultural plantations. Livestock also suffers, with reports indicating that 5 million chickens died during the 2015 heat wave in Telangana alone.

Water resources face unique challenges during cold spells. Water bodies may freeze during prolonged cold waves, affecting community water availability. Regions unaccustomed to extreme cold face particular difficulties as their infrastructure and resources are often inadequately prepared for such conditions. The socioeconomic impacts can persist long after temperatures return to normal, especially in areas with limited heating infrastructure and vulnerable populations.

Climate change and future projections

The frequency and intensity of heat waves are increasing due to climate change. According to research, heat waves in India are projected to occur thirty times more often by the end of the century if global mean temperature increases by 2 degrees Celsius. Under high-emissions scenarios, annual heat-related deaths could increase 25-fold by 2100, potentially reaching over 1.5 million deaths per year.

Conversely, cold wave frequency and duration have shown decreasing trends in most parts of northern India due to rising winter minimum temperatures associated with global warming. However, this trend varies regionally, and some areas still experience severe cold events that catch unprepared communities off guard.

What do you think? How can India better prepare its healthcare systems and vulnerable communities for the increasing frequency of extreme temperature events? What role should local governments play in implementing heat and cold action plans to reduce mortality from climate extremes?

References

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Table of Contents

Heat waves: When temperatures cross dangerous thresholds 🔗

Geographic distribution and timing 🔗

The deadly toll of extreme heat 🔗

Underreporting and actual burden 🔗

Cold waves: The silent winter threat 🔗

Vulnerable regions and populations 🔗

Health impacts of extreme cold 🔗

Cardiovascular and respiratory stress 🔗

Broader socioeconomic impacts 🔗

Climate change and future projections 🔗