Data: Heatwave kills in India, but agencies can't agree on numbers, methodology

In 2023, 68 people died in the Ballia district of Uttar Pradesh as temperatures reached 43.5 degree Celsius. Despite the doctors’ claims of deaths due to heat, authorities only reported two deaths due to heat stroke. The top administrative official of Ballia said that it was difficult to say if the deaths were due to heatwaves.

A total of 252 deaths were reported in the first half of 2023 (till June 30) across India, up from only 33 fatalities in the same period last year as reported by the Ministry of Health and Family Welfare. However, media reports said that over 96 people died due to heatwave conditions across only two of India’s most populous states over just a few days. Along with the deaths in Ballia, over 26 people died in Uttar Pradesh’s Deoria from heat related illnesses. 

Data on heatwave deaths has always been unclear – in 2010, the heatwave in Ahmedabad led to the deaths of over 800 people due to heat strokes, however, the number of deaths reported was only 58 all across Gujarat as per the NCRB report (2010). This shows a clear and enduring underreporting of deaths due to heat waves in the country. The problem lies in data and methodology ambiguity and a multiplicity of government agencies recording heat-related deaths in the country.

Official records by various agencies like the Indian Meteorological Department (IMD), Ministry of Health and Family Welfare, the Press Information Bureau (PIB), EnviStats Report which is published by the Ministry of Statistics and Programme Implementation, and the National Crime Record Bureau (NCRB) release data on deaths due to heat, but this data is often in contradiction with each other along with data coming from media reports. There are significant discrepancies in recording deaths due to heatwaves by these agencies, leading to large gaps in key information needed to combat heatwaves successfully. 

The NCRB provides data on deaths due to extreme weather events including deaths from heat/ sun stroke in their annual report Accidental Deaths and Suicides in India. The IMD provided data on deaths due to heatwaves in 2022 in their Annual Statement on Climate and their Annual Report on Climate. 

Defining Heat waves

A Heatwave is a period of abnormally high temperatures, more than the normal maximum temperature. It is a condition of air temperature which, when exposed to, becomes fatal to the human body. The extreme temperatures and resultant atmospheric conditions adversely affect people living in these regions as they cause physiological stress, sometimes resulting in death. The Indian Meteorological Department (IMD) defines it based on the temperature thresholds over a region in terms of actual temperature or its departure from normal. In certain countries, it is defined in terms of the heat index based on temperature and humidity or based on the extreme percentile of the temperatures. Other agencies depend on the IMD to define a heatwave.

The IMD has given the below criteria for defining heatwaves in India:

• Heatwave is considered if the maximum temperature of a station reaches at least 40 degrees Celsius or more for Plains and at least 30 degrees Celsius or more for Hilly regions.

• Based on departure from normal: Heatwave is considered if the temperature departure from normal is 5°C to 6°C. A severe Heatwave is considered if the departure from normal is 7°C or more. 

• When the actual maximum temperature remains 45°C or more irrespective of normal maximum temperature, heatwaves should be declared. 

How Each Agency Collects Heatwave Data and Records Deaths

The IMD has a large network of surface observatories across the country to measure various meteorological parameters like temperature, relative humidity, pressure, wind speed, etc. Based on daily maximum temperature station data, the normal maximum temperature data for a day for a particular station is garnered based on the data between 1981 to 2010. As per the IMD’s definition of a heatwave, it declares the same over a region. Once a heatwave is declared, it is published in the India Weather Forecast Bulletin. The heatwave information is shared with the state government and media along with the health department and the power sector.

The NCRB annual report on accidental deaths and suicides uses data furnished by state police departments and published in the EnviStats, with heat/ sunstroke as the cause of death. 

Heat related illnesses are now documented by the Integrated Health Information Platform, by the National Programme on Climate Change and Human Health. To ascertain if a death is due to heat, there exist guidelines on investigating suspected heat related illness death as published by the National Centre for Disease Control (NCDC) under the Ministry of Health and Family Welfare.

Inconsistencies in Data

EnviStats India Report for 2022 published by the Ministry of Statistics and Programme Implementation reported the number of deaths due to heatwaves between 2001 to 2021 as given in Table 1. Moreover, it reports a total of 17,488 deaths due to heatwaves since 1970. 

Table 1: Deaths Due to Heatwaves in India (2001 - 2021)

Fig 2: Deaths due to Heatwaves in India between 2001 to 2021. Source: EnviStats India Report for 2022

Fig 1: Number of Deaths due to Heatwaves as reported by Various Agencies between 2015 to 2022. Source: NCRB Accidental Deaths and Suicides in India, Ministry of Health and Family Welfare, Indian Meteorological Department, EviStats Report 2022, and NDMA

As per the Indian Meteorological Department (IMD) reports, for 2021, there were no heatwave deaths recorded. Moreover, Heatwaves were not a category of Extreme Weather Events which included Cyclones, Floods, Heavy Rains, Lightning and Thunderstorms, and Other Events (Cold Waves, Dust Storms, Gales, Hailstorms, and Snowfall), until their Statement on Climate released in 2022. However, the National Crime Records Bureau (NCRB) reported 374 deaths due to heat/sun stroke in 2021. Concurrently, the Ministry of Statistics and Programme Implementation through their EnviStats India 2022 Report disclosed that no people had died due to heatwaves in 2021.

However, for 2022, the IMD first included Heat waves as an Extreme Weather Event, reporting a total of 30 deaths across states with most deaths from Maharashtra and Odisha (13 and 12 respectively – all reported during the period between March to April 2022). The EnviStats report disclosed 27 deaths due to heatwaves in the same year. Compared to the NCRB data for 2022, there seems to be a huge discrepancy in the number of heat deaths, as it reported 730 deaths due to heat/sunstroke. 

Of the 24 listed states/UTs, 18 reported numbers, and in 2022, only 7 states/UTs of the listed reported data. 

Delving deeper into the data reported by states, as per the Ministry of Health and Family Welfare, Delhi has reported 0 deaths between 2015 to 2022, and only 1 death due to heat/sun stroke in 2023 (until 30 June). The Press Information Bureau (PIB) reported 5 deaths in Delhi in 2015.

2015 was a deadly year for Indians bearing the brunt of heat-stress – with casualties abnormally high with most of the deaths concentrated in Andhra Pradesh, Telangana, Odisha, Punjab, Uttar Pradesh, and Bihar (see Table 3). 

Table 3: Number of Heatwave Deaths reported State-wise in 2015

One can see the deviation and inconsistency between the figures reported by various agencies. The number of deaths by heat waves reported by the NCRB is half the number of fatalities reported by the PIB in Andhra Pradesh in 2015. Inversely, the number of deaths reported in Uttar Pradesh in 2015 due to heatwaves by the PIB is minuscule compared to the data released by the NCRB. The state of Odisha has reported similar figures by all three agencies, however it is an exception. Other states have not released data under the PIB or Ministry of Health and Family Welfare.

As per the Ministry of Health and Family Welfare, Gujarat reported 17 deaths in 2015 due to heat/sunstroke, while the Press Information Bureau (PIB) reported only 10 deaths. At the same time, the NCRB reported 52 deaths due to heat stroke. The Gujarat State Disaster Management Authority (GSDMA) reported 58 deaths due to heatwaves, while media reports (see Table 4). The GSDMA also reported that the number of deaths reported across the state were 58, 446, 463, and 775 respectively between 2015 to 2018, which showed an increasing trend of the deaths.

Table 4: Number of Heatwave Deaths reported in Gujarat

Andhra Pradesh reported varying discrepancies in numbers as well, with an extremely high number reported in comparison to other states. The state reported 1369 deaths due to heat/sun stroke in 2015 as per PIB, while the Ministry of Health and Family Welfare declared 1422 deaths, and media reports announced 1735 deaths due to heatwaves. At the same time, the National Crime Record Bureau reported 654 deaths due to heat/ sun stroke (see Table 5). The numbers dropped to 0 deaths in 2020 and 2021, and only 1 death in 2022 as per the Ministry of Health and Family Welfare.

Table 5: Number of Heatwave Deaths reported in Andhra Pradesh

The case of Telangana too is rather curious with inconsistencies showing up in the data. Both the PIB statement and the Ministry of Health and Family Welfare reported 541 deaths from heat waves in 2015, and the media too reported a comparable figure of 585 deaths. However, the NCRB reported only 182 deaths due to heat/sunstroke in the year (see Table 6).

Table 6: Number of Heatwave Deaths reported in Telangana

Human casualties are a crucial measure of loss and damage caused by heat waves, a major extreme weather event associated with climate change. A significant indicator for the Sustainable Development Goal (SDG) 13 on climate change is deaths due to extreme events.  But the Indian healthcare system struggles with recording and collating data at the local level, since heat related deaths are recorded by the local police station and the municipalities. These statistics are crucial in recording the effects on human life due to extreme heat events.      

To add to this, there is the challenge of what is classified as a heat-related death. Heat stroke deaths are classified as direct deaths (due to exertion under direct sunlight) and indirect or non-exertional deaths (people who suffer a heat stroke due to high ambient temperatures). Indirect deaths are noticed mostly among people with comorbidities. The IMD and NCRB  only record heat-stroke-related deaths during periods of extreme heat. This narrow definition of heat related stress and mortality and description of the circumstances of death due to heatwave means these authorities record only direct deaths. Only deaths due to heat/ sun stroke are attributed under the National Crime Record Bureau annual report on Accidental Deaths and Suicides in India. Dileep Mavalankar, director of the Indian Institute of Public Health (IIPH) said that “Heat wave deaths are like an iceberg… 90% [which are indirect deaths] is not visible”. 

The public health system should look for excess than usual mortality during heat waves and not only deaths due to heat strokes. It is important to compare every day mortalities with past numbers and explore if heat is playing an outsized role in deaths. There is also a need to co-relate the number of daily deaths with the temperature and humidity for that day and the preceding few days to know if mortality rises during the heatwave or not. Thus, it becomes important to compare every day mortalities with past numbers and explore if heat is playing an outsized role in deaths. 

Given the clear discrepancies and inconsistencies in the data, it is clear that India has a long way to go in adequately preparing for and building resilience to heatwaves. 2023 was the hottest year on record. As heat wave break records in India and are expected to increase in both occurrence and duration, it’s important to close the data gap and expand preparedness.