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Understanding The Metrics of Heat Waves in South Asia

Credits: NASA/JPL-Caltech

The prolonged exposure to high temperatures and wet bulb conditions can lead to high risks of heat stroke and a range of physiological impacts. 90 deaths were reported in 2022 due to extreme heat stress.


By Salam Rajesh

Climate change has made devastating heat wave impact early in India and Pakistan this year, with Pakistan experiencing 30 times more intensity than India, says Dr Friederike Otto of the World Weather Attribution, adding that climate change is likely to increase extreme monsoon rainfall, flooding highly vulnerable communities in Pakistan.

Dr Otto (Senior Lecturer, Grantham Institute for Climate Change and Environment & Co-Founder, World Weather Attribution) was speaking on the topic ‘Understanding Attribution Science: Human induced Climate Change and Heatwaves’ as part of the proceeding of a National Workshop on Heatwaves, Climate Change and its Impacts on Health, Economy and Energy Policies in India at Bengaluru on the 27th of last month, courtesy of Bangalore-based climate strategist group Climate Trends.

Dr Otto’s observation reflects closely to the World Meteorological Organization (WMO)’s warning of a likely spike in temperatures globally this summer, as prelude to the projected El Nino event this year. The year 2015-2016 was recorded as the hottest year in recent history, and this was primarily driven by an El Nino event according to reports. 1500 deaths were reported in the coastal plains of Odisha during 2015 from the intense heat wave that year.

In March, the India Meteorological Department (IMD) had predicted normal monsoon this year but forewarned that an El Nino event can affect the monsoon. Forecasting a 75 percent chance of El Nino in India, the IMD said it could weaken the southwest monsoon and may lead to severe heat waves and droughts in the country – a forewarning that could wreak havoc with the agricultural system in the country, and with a possible backlash on the rural economy.

The forecast for the year has disturbing news for the country wherein compound events of heat waves, cyclones and floods can overlap one another and can cause extensive damages to crops and properties, asserts scientist Dr Roxy Mathew Koll of the Indian Institute of Tropical Meteorology, Pune. Dr Koll was speaking on the subject ‘The dominance of Climate Change on global circulations and its impact on heatwaves and marine heatwaves’.

Bangalore-based climate strategist group Climate Trends stated that “By February-April 2023, most models indicate the return of ENSO-neutral, with a probability of 82%. What is more concerning is the arrival of the dreaded phenomena of El Nino. Climate models are predicting potential return to El Niño by May-July, which coincides with summer monsoon that spans from June to September”.

“During a La Niña, the tropical Pacific soaks up heat like a sponge and builds up the warm water volume. This is the warm water that spills across from the western Pacific to the eastern Pacific during an El Niño. Three consecutive years of La Niña means that the warm water volume is fully loaded and it is likely that the system is ready to give birth to an El Niño. Will it be a strong El Niño like the one during 2015-16? We may get some indications in spring itself,” explains Dr Raghu Murtugudde, Visiting Professor, Earth System Scientist at IITB (Indian Institute of Technology, Bombay) and Emeritus Professor at University of Maryland.

“As for the monsoon itself, if an El Niño state does emerge by summer, then we are more than likely to see a deficit monsoon. A transition from a La Niña winter (which we are in now) to a summer El Niño state tends to produce the largest deficit in the monsoon – of the order of 15%. This implies that the pre-monsoon and monsoon circulations tend to be weaker”. Dr Raghu was speaking on the thematic topic ‘Understanding the variation in weather patterns and the need for early warning systems’.

Kunal Satyarthi (Joint Secretary, National Disaster Management Agency) speaking on the topic ‘The hurdles in building adaptive capacity: A status check on planning and implementation of heat action plans’, stressed on the triple risks of climate hazard, vulnerability and exposure that can cause extensive damage and loss across the different sectors, with the marginalized sections of society more likely to be impacted by the risks involved.

Dr Luke Parsons (Postdoctoral Associate, Duke University) speaking on the subjective matter, ‘Rising wet-bulb temperatures and labour impact’, stressed that as per the Wet Bulb Globe Temperature (WBGT) model, the International Organization for Standardization (ISO 7243) emphasizes that during temperatures reaching above 26 degree Celsius workers are advised to take half hour rest from their heavy work duty.

In case of temperatures reaching above 32-33 degree Celsius the ISO recommends all heavy works should stop. The WBGT model is used in military, occupational health, and athletic events, Dr Luke explains while stating that the model includes temperature, humidity, wind speed, and sun exposure.

The average highest Wet Bulb Globe Temperature for South Asia during 2002 to 2021 was experienced in the north-western parts and the northern plains of India, Pakistan and in Bangladesh, observed Dr Luke, with temperatures reaching 34 degree Celsius and above.

Calculating on the WBGT model, an estimation of the productivity loss across the world reveals a massive global total loss of around 220 billion hours per year, says Dr Luke. Calculating the estimate total labour hours lost per year for different countries, India loses 101 hours per year – almost equivalent to the loss of around 23 million jobs.

Following India is China with 21 hours, Bangladesh with 14, Pakistan with 13, Indonesia with 10, Sudan and Viet Nam with 7, Nigeria and Thailand with 6, and Philippines with 5 hours of labour lost per year respectively.

On this footnote, Climate Trends noted that, “While 2022 set a record with 200 heatwave days in India with some of the hottest months since 1901 and impacting nearly 70% of the country, spring went missing in 2023 as well. February this year was declared the hottest in the last 123 years, the first ever since 1901. March saw heatwave in isolated pockets but April began on a hotter note, with mercury rising every day. State-run India Meteorological Department (IMD) already predicted an increased probability of heatwaves during April and May”.

This comes with a fair indication that unless Heat Action Plans for every States are formulated well in time, things may go from bad to worse. “In a country like India, which is densely populated, the extreme heat hits the poor the hardest who are working as urban or rural labour without access to cooling. The prolonged exposure to high temperatures and wet bulb conditions can lead to high risks of heat stroke and a range of physiological impacts. 90 deaths were reported in 2022 due to extreme heat stress”, forewarns Climate Trends experts.

(The writer looks at environmental stories through the journalistic lens. He can be reached at [email protected])

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