Heat waves will intensify, milder ones are also deadly, scientist makes pitch to NDMA

The health impacts of heat waves can range from mild symptoms like dehydration and heat cramps, characterised by edema and syncope with fevers below 39°C (102°F), to severe conditions such as heat exhaustion and heat stroke.

As India gears up for the 2024 Lok Sabha elections, the focus isn’t just on electing chosen leaders but also on navigating the severe challenges posed by unprecedented heat and climate anomalies.

Dr Roxy Koll, a scientist at the Indian Institute of Tropical Meteorology (IITM) Pune, in his presentation to the National Disaster Management Authority (NDMA) during a national workshop on heat waves earlier this month, shared insights on severe heat conditions during the month of April 2023 and current projections that set a grim backdrop for the 2024 elections.

A 20°C night-time temperature gap in Delhi

Highlighting a stark temperature disparity for night temperatures—up to 20 degree Celsius difference between urban and rural areas in Delhi and surrounding regions for the month of May 2022, Dr Koll shared insights during the NDMA workshop emphasising this stark contrast due to the urban heat island (UHI) effect.

“Climate change is aggravating the heat everywhere but the urban heat islands that trap this heat are our own construction. The UHI effect is most visible in the night-time temperatures. Cities turn into urban heat islands when buildings, roads, and other infrastructure absorb and re-emit heat, causing cities to be several degrees hotter than surrounding rural areas,” said Dr Koll.

During the day, however, the sun’s rays reach as shortwave radiation and heat the Earth’s surface. “At night, the heat escapes as longwave radiation. While shortwave radiation can easily penetrate through and reach the surface, the longwave gets trapped easily by concrete and clouds,” he said.

The high-rise buildings and concrete setups in the cities do not let the excess heat escape during the night. As the temperatures do not cool down, the heatwave continues into the night. “Open green spaces and natural environments with trees can help release the heat faster during the night. However, in India, we do not appreciate natural space as much as we appreciate skyscrapers. Add some haphazard city planning, poor architecture and unsustainable construction to it, and the recipe for an urban heat island is complete,” said Dr Koll.

He also highlighted a similar increase in heat pockets due to the Urban Heat Island UHI effect from 2001 to 2021 in major Indian cities, including Delhi, Kolkata, Hyderabad, and Bangalore.

“This analysis shows the expanding footprint of UHI and its exacerbating impact on urban temperatures, urging a reconsideration of urban development and green space integration to mitigate these effects,” said Dr Koll.

“As we approach national elections, it’s vital that the Election Commission of India (ECI) recognises the threat posed by heatwaves and takes decisive action,” said Dr Dileep Mavlankar, former director, the Indian Institute of Public Health-Gandhinagar. “Ensuring that election rallies, public gatherings, polling stations, and any other election-related events are equipped with cooling stations, ample shade, water stations, and medical facilities is critical for protecting the electorate. Specific recommendations and awareness campaigns are needed to emphasise the importance of hydration and the signs of heat-related illnesses need to be made by ECI across every region.”

The impending heat wave challenge

“We need to realise that heatwaves are going to intensify in terms of the frequency, intensity, duration, and the area covered. This means that we need to be perpetually prepared for the heat stress from February to June in India. We should have policies with long-term vision in place that can protect our lives and livelihoods as the temperature rises,” said Dr Koll, adding that it is crucial that citizens observe the heatwave forecasts that the India Meteorological Department (IMD) will start disseminating from March onwards.

Dr Mrutunjay Mohapatra, director general, IMD said, “Starting March, IMD will release forecasts in our standard pattern, offering daily temperature forecasts over five days, along with biweekly and seasonal outlooks. These forecasts will comprehensively cover temperature, wind speed, humidity, and the heat index among other key parameters, ensuring citizens have full access to essential weather information for their daily lives, safety, and plan any movement according to advisories.”

The World Meteorological Organization (WMO) has indicated that the ongoing El Niño event (a climate phenomenon characterised by the periodic warming of sea-surface temperatures in the central and eastern Pacific Ocean, affecting global weather patterns), expected to last at least until April 2024, will contribute to a further spike in temperatures both on land and in the ocean, exacerbating extreme weather conditions such as heatwaves, floods, and droughts. This phenomenon, alongside the record high land and sea-surface temperatures observed since June 2023, suggests that 2024 maybe even warmer, potentially surpassing 2023 as the warmest year on record due to the combined effects of El Niño and human-induced climate change.

“The El Niño is set to weaken by April–May and transition to La Niña (cooling of sea-surface temperatures in the central and eastern Pacific Ocean, influencing global weather patterns with effects often opposite to those of El Niño) conditions by June. While El Niño is still active, global and Indian temperatures may continue to be high at least until the start of May,” said Dr Koll. The effects of La Niña are asymmetrical compared to the El Niño. “Recent La Niña years were hot and had some of the strongest heatwave events. However, the chances of a delayed monsoon are generally less if the La Niña teleconnection is strong,” added Koll.

How this impacts our body

The human body’s tolerance to heat varies significantly across India, influenced by regional climatic conditions, humidity levels, and acclimatisation. In regions like the arid northwest, residents are adapted to high temperatures, while in the humid coastal areas, even lower temperatures can feel intolerable due to high humidity.

The IMD defines a heat wave as a period of abnormally high temperatures, surpassing the normal maximum temperature, primarily observed during the summer season from March to June, and occasionally extending into July.

The criteria, set by IMD, for declaring a heat wave vary based on geographical and climatic conditions. For plains, a heat wave is not considered until the maximum temperature reaches at least 40 degrees Celsius, and for hilly regions, the threshold is at least 30 degrees Celsius. A heat wave departure from normal is categorised as 5 degrees Celsius to 6 degrees Celsius for areas where the normal maximum temperature is less than or equal to 40 degrees Celsius, and a severe heat wave is declared when the departure from normal is 7 degrees Celsius or more.

In contrast, for regions where the normal maximum temperature exceeds 40 degrees Celsius such as Churu in Rajasthan or Nagpur in Maharashtra, a heat wave is acknowledged with a departure from normal between 4°C and 5°C, and a severe heat wave with a departure of 6°C or more. Additionally, when the actual maximum temperature remains at 4 to 5 degree Celsius or above, irrespective of the normal maximum temperature, heat waves are declared.

“We also need to take into account that some of these heat waves are overlapping with other climate extremes such as droughts or rainfall deficits, wildfires, and air pollution that when combined threaten the health of the population and also impact the food, water and energy security of the country,” Koll said.

On April 16, 2023, during a public event in Kharghar, Navi Mumbai in Maharashtra, a tragic incident occurred due to extreme heat, offering a sombre lesson in the lead-up to the 2024 elections. According to the district collector’s office, at least 14 people died, and another 600 suffered from heat stroke after being exposed to the sun for over six hours.

In his presentation, he highlighted the lethal synergy of high temperatures, elevated humidity, and prolonged exposure among vulnerable populations. The combination of high temperatures, recorded between 34-38 degrees Celsius by nearby meteorological observatories on the day, and a significant humidity level of 45%, created perilous conditions, said Dr. Koll. “When the air has high levels of humidity along with the heat, the body fails to regulate its internal temperature via sweating as it does not evaporate fast enough,” he said.

“Though the heat is blamed, it is the lack of basic precautions that saw them die,” Koll said, pointing out the critical need for awareness and preventive measures against heat-induced health emergencies. “Hazards like heat waves become lethal when the most vulnerable sections of the population are exposed to it for prolonged periods.”

The health impacts of heat waves can range from mild symptoms like dehydration and heat cramps, characterised by edema and syncope with fevers below 39°C (102°F), to severe conditions such as heat exhaustion and heat stroke. “Heat exhaustion symptoms include fatigue, weakness, dizziness, and excessive sweating. In more severe cases, heat stroke can occur, with body temperatures soaring above 40°C (104°F), leading to delirium, seizures, or even coma, marking it as a potentially fatal condition,” said Dr Pradeep Awate, assistant director, Maharashtra Health Services.

A study on heatwaves and mortality

Insights from a recent study published in the peer-reviewed journal Environment International, “Impact of heatwaves on all-cause mortality in India: A comprehensive multi-city study”, by Jeroen de Bont and his team at Karolinska Institutet along with authors from India reveal the underestimated mortality risks posed by milder heat waves.

The research offered a comprehensive overview of heatwave patterns across different Indian cities, detailing the mean daily deaths, the number of heatwaves, annual frequency, and other critical metrics such as the average start day of the heatwave season, length, and intensity of heat waves.

The study found a significant association between heatwaves and increased all-cause mortality across 10 Indian cities, with an estimated 14.7% rise in daily mortality during heatwaves. Annually, approximately 1,116 deaths were attributable to heatwaves. The study also assessed variations in daily deaths, the number of heatwaves, and their intensity from 2008 to 2019.

Key takeaways include Ahmedabad experiencing 28 heatwaves with an average of 122 daily deaths, and Delhi facing 19 heatwaves with 284 daily deaths, highlighting significant regional differences. The intensity of heatwaves varied, with cities like Delhi experiencing higher temperatures (37.7 degree Celsius) compared to Shimla (26.5 degrees Celsius). Cities like Hyderabad and Pune showed a higher frequency of heatwaves per year, with Hyderabad experiencing an average of 4.0 heatwaves annually and Pune 4.3.

In contrast, cities like Chennai and Varanasi had a lower annual frequency, at 2.2 each. The intensity of heatwaves varied significantly across cities, with Shimla experiencing milder conditions (26.5 degree Celsius) compared to the more intense heat waves of Varanasi (37.6 degree Celsius).

The less severe heat waves turned out to be more fatal, with fatalities inversely related to the heatwave’s severity and length, the study said. This pattern suggests that milder heat events, being more frequent, end up being more deadly than the rarer extreme heat waves. As a result, it might be prudent to consider issuing heat warnings at lower temperature thresholds to ensure broader public safety, the study suggested.

This variability underlines the importance of localised heat action plans and awareness to mitigate heat-related health risks, especially in identified heatwave hotspots across the country, said Mavalankar.

“It is thus also important to consider the timing of elections and consider shifting them to winter months to ensure public gatherings are less exposed to high temperatures. Adequate preparation and infrastructure can make a significant difference in voter safety and turnout,” he added.

Koll added, “Considering the latest projections, by the mid-21st century, we anticipate about 2.5 heatwave events per season, escalating to around 3.0 by the century’s end, under the moderate emission scenario. Simultaneously, the average total duration of these heat waves is expected to extend to approximately 15 days in the coming decades, and further to 18 days towards the century’s close. This trend underscores an urgent need for robust climate resilience and adaptation strategies to protect our communities.”

The NDMA has identified that higher daily peak temperatures and longer, more intense heat waves are becoming increasingly frequent globally due to climate change. As part of our annual preparedness efforts, the NDMA will be issuing advisories across all relevant departments and across states (ahead of the summer season). We will approach this task with an increased sense of urgency, recognising the critical importance of timely and effective response measures to safeguard the health of citizens,” NDMA member secretary Kamal Kishore said.

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